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Letters |
Clin. Chem. Lab.,
1
Lab. of Endocrinol. and Toxicol., Azienda Ospedaliera Careggi Firenze, Firenze, Italy,
2
Dept. of Clin. Pathophysiol., University of Firenze, Firenze, Italy
a Address correspondence to this author at: Lab. di Endocrinol., Azienda Ospedaliera Careggi, Largo Palagi 1, 50139 Firenze, Italia.
To the Editor:
Adult intestinal alkaline phosphatase (IAP) isoenzyme has long been known to be a minor component of serum alkaline phosphatase (ALP). On electrophoresis it migrates in the ß-globulin position and is detectable at low activity (<20% of total ALP) in ~20% of sera from healthy individuals (1). Increased IAP activity has been reported in chronic renal failure (55%), liver cirrhosis (46%), and diabetes (54%) (2). Moreover, subjects with blood groups O and B have also been reported to have increased serum IAP activity, especially in postprandial samples after a fatty meal (3). A high percentage of IAP-positive samples has been shown to contain an IAP "variant" form displaying similar enzymatic activity but different electrophoretic mobility (1).
We measured ALP isoenzymes in a population of healthy obese subjects (n = 76; age 40.8 ± 14.9 years, mean ± SD) periodically monitored because of familial diabetes history by means of a conventional electrophoretic method (4). Serum IAP was present in 51% (39 of 76) of the subjects and most of these samples (29 of 39) contained the variant form of the IAP (74%). The latter form was never detectable in any IAP-negative sample, as already reported by others (2).
The IAP-positive and -negative subgroups were then compared in
terms of body mass index (BMI) and some serum components (total ALP,
glucose, insulin, C-peptide, triglycerides, cholesterol). Significant
differences between the subject groups were apparent neither in the BMI
nor in the fasting basal values. However, when the response to the
standard oral glucose tolerance test (OGTT) (75 g) was considered
(two-way ANOVA split-plot design), glucose (P <0.01),
insulin (P <0.05), and C-peptide (P <0.01) were
higher in the IAP-positive groups than in the negative one (Fig. 1
). Such a difference was increased when considering only the IAP
variant-positive group. However, no correlation was apparent between
the IAP activity and the OGTT response. On the other hand, the IAP
variant activity was significantly correlated to the response of
insulin to OGTT (P <0.05, Spearman test). Despite a
positive trend, no significant correlation could be proved for the
glucose and C-peptide responses.
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We can thus conclude that: (a) the percentage of serum IAP-positive samples in a population of obese subjects with familial diabetes history is increased (51%); (b) ~74% of the IAP-positive samples contain an IAP variant; and (c) the IAP-positive subjects, and particularly the IAP-positive/variant-positive ones, showed a significant increase in insulin secretion with respect to the IAP-negative subgroup.
Such conclusions suggest a possible linkage between IAP activity and glucose metabolism, namely, that IAP could play an important role in the fasting–feeding stages. A similar hypothesis has been formulated by other authors (5) with regard to diabetic subjects.
References
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