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Letters |
1 Service de Biochimie C and
2 Service d’Anatomie et Cytologie Pathologiques (Pr F. Capron) Groupe Hospitalier Pitié-Salpêtrière 47-83 bd de l’hôpital 75651 Paris Cedex 13, France
aAuthor for correspondence. Fax 33-1-4217-7616; e-mail jean-louis.beaudeux{at}psl.ap-hop-paris.fr.
To the Editor:
S-100B is expressed by cells of neuroectodermal origin, particularly cerebral glial cells (astrocytes), and in several tumor processes, including malignant melanocytic lesions (1). Although S-100B is localized primarily in the intracellular compartment, it is physiologically detectable in biological fluids (cerebrospinal fluid, serum, and urine). Measurement of S-100B has been proposed as a biological marker of brain damage, e.g., head injury, cerebral hypoxia, and stroke (2), and of malignant melanoma(3). Serum S-100B values in healthy individuals range from 0.02 to 0.15 µg/L, as determined by immunoluminometric analytical methods. Although studies are controversial, S-100B concentrations in biological fluids appear to be age- and sex-dependent (4)(5)(6)(7). No information is available regarding potential differences according to the race or ethnicity of individuals.
Here we report the results of a study to determine the influence of race on serum S-100B concentrations. Blood samples were taken from 136 healthy individuals, divided into three groups according to race: black (B), Asian (A), and Caucasian (C). All individuals gave informed consent for participation in the study. The three groups did not differ significantly in sample size (n = 46, 44, and 46 for groups B, A, and C, respectively), mean (SD) age [45 (11), 49 (13), and 49 (14) years; not significant], or M/F ratio (28/18, 25/19, and 24/22 for groups B, A, and C, respectively). Blood was collected in Vacutainer® Tubes and centrifuged within 2 h (1000g for 10 min); serum samples were then frozen at -20 °C until assayed (within 2 months). S-100B concentrations were determined with an immunoluminometric sandwich assay on a LIAISON analyzer (Diasorin Laboratories) with the manufacturer’s reagents. All determinations were performed in duplicate.
The results of these analyses are shown in Fig. 1
. Mean (SD) values for serum S-100B were significantly higher in groups B and A compared with group C [0.14 (0.08), 0.11 (0.08), and 0.07 (0.03) µg/L for groups B, A, and C, respectively; P <0.001]. Median values also showed similar differences between the groups: 0.12, 0.09, and 0.06 µg/L, for groups B, A, and C, respectively (P <0.001 between B and C and between A and C). Serum S-100B concentrations did not differ significantly between groups B and A, although a trend to statistical significance was noted (P = 0.064). Finally, the number of healthy individuals having a serum S-100B concentration above the recognized pathologic cutoff value (0.15 µg/L) was 14 of 46 (30%), 9 of 44 (20%), and 1 of 46 (2%) for groups B, A, and C, respectively.
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Our data indicate that healthy black and Asian individuals have higher serum S-100B concentrations than do Caucasians. We hypothesize that these differences in serum S-100B according to skin color may be related to increased expression of this protein by healthy melanocytes in blacks and, to a lesser extent, in Asians, compared with Caucasians. Melanocytes from black individuals have been shown to have a higher metabolic activity than those from Caucasians, including increased melanin synthesis (8). To our knowledge, there are no in vitro experimental data available regarding S-100B protein expression and release according to the origin of melanocytes (i.e., black, Asian, or Caucasian individuals); we believe that the S-100B protein subunit might be more highly expressed in black and oriental races and that this higher expression could explain the higher concentrations of circulating S-100B observed in healthy black and Asian individuals. In vitro experimental data are also lacking for determining the involvement of S-100B expression and release by healthy melanocytes in the physiologic serum concentrations of this protein, especially with respect to skin color. Our results clearly indicate that the racial origin of patients should be taken into account when interpreting serum S-100 concentrations as an indicator of brain damage or malignant melanoma.
References
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