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Letters |
1
Clin. Biochem. and
2
Endocrinol. Unit, Dept. of Clin. Pathophysiol., Viale Pieraccini, 6, 50139 Florence, Italy,
3
Inst. of Gerontol. and Geriatrics, Univ. of Florence, 50139 Florence, Italy
a Author for correspondence.
To the Editor:
Free radicals are considered important factors in biological aging (1). Consequently, there is increasing interest in the mechanisms of antioxidant protection against free-radical-induced injury and in identification of suitable biochemical indicators for measuring serum antioxidant capacity (SAC) (2). Several methods have been proposed for the measurement of SAC, including the enhanced chemiluminescence assay used in this study (3). This technique is calibrated with TroloxTM, a water-soluble vitamin E analog (Hoffmann–La Roche, obtained from Aldrich Chemical Co., Gillingham, Dorset, UK), and assay results are expressed as µmol/L Trolox equivalents.
We measured serum SAC in 58 healthy subjects: 37 adults (19 men and 18 women, age range 18–91 years) and 21 centenarians (4 men and 17 women, age range 100–105 years). None of the subjects was taking drugs. All subjects gave a full social and medical history and underwent physical examination. Elderly subjects (>65 years) were selected by the criteria of the Eurage Senieur protocol (4). In particular, all centenarians were mentally competent to give oral and written informed consent.
We observed a statistically significant difference in SAC values
between adults and centenarians; SAC values were significantly
decreased in centenarians (306.2 ± 108.0 vs 493.0 ± 183.4
µmol/L Trolox equivalents, P <0.001) (Fig. 1
A). The chemiluminescent method used in this study, however,
does not indicate which biochemical changes are responsible for this
reduced antioxidant capacity in healthy centenarians. Several factors,
including urate, ascorbate, vitamin E, bilirubin, and thiols, have been
reported to affect SAC (5)(6). We evaluated
serum urate and bilirubin. Serum urate concentrations, which usually
account for 60–70% of SAC (5)(6), were
unchanged in our centenarian subjects when compared with the healthy
adults (254.3 ± 66.6 µmol/L vs 269.4 ± 70.3 µmol/L,
mean ± SD, P not significant) (Fig. 1B
). Total
bilirubin was significantly reduced (healthy adults 13.5 ± 5.7
µmol/L, centenarians 9.2 ± 4.2 µmol/L, P <0.01)
(Fig. 1C
). However, the relation between urate and SAC is maintained,
as demonstrated by correlation studies both in healthy adults
(y = 1.773x + 15.4, n = 37,
r = 0.698, P <0.001) and in centenarians
(y = 1.274x - 19.0, n = 21,
r = 0.913, P <0.001). Similarly, we
observed a statistically significant correlation between total
bilirubin and SAC in all the subjects (y =
15.885x + 199.535, n = 45, r = 0.519,
P <0.001).
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In conclusion, reduced SAC in centenarians seems determined by the decrease of at least some serum antioxidants such as bilirubin, but not by urate. Moreover, during the interview and clinical examination, the centenarians reported reduced appetite and nutrient intake, which can influence the concentration of serum antioxidants such as ascorbate and vitamin E. If we consider that urate is an efficient antioxidant only for some kinds of free radicals (7) and thus is unlikely to provide an adequate antioxidant defense if other antioxidant systems are deficient (8), the reduced SAC in healthy centenarians can be more relevant than the absolute value of SAC reduction.
Whether reduced antioxidant capacity in centenarians plays any pathophysiological role in the aging process and whether supplementary antioxidant therapy might extend life span remain to be clarified.
References
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