Lublin, Poland.
Sir,
Despite persisting methodological and interpretational controversies, the PTHcalcium relationship curve has been accepted by many authors as a method of investigating the dynamic status of parathyroid glands in haemodialysis patients [1,2]. Since increased secretion of IL-1, IL-6 as well as TNF- stimulates bone resorption in vitro [3,4], these cytokines may play a significant role in the pathogenesis of renal osteodystrophy [36]. The aim of our study was to establish possible relationships among IL-1, IL-6, TNF-
, and PTHcalcium curve parameters in haemodialysis patients with severe hyperparathyroidism, and to determine if calcitriol can modify these relationships.
Eleven haemodialysis patients with a serum i-PTH level over 1000 pg/ml and a serum aluminium level <10 µg/l were studied. Haemodialysis patients who were dialysed three times a week were given i.v. calcitriol at the end of each dialysis session. In the first month the received 1 µg per session, then 1.5 µg in the following month, and a mean of 2.1±0.9 µg according to CaxP product in the 3rd month (not to exceed 70 mg/dl). Both before and after 3 months of calcitriol therapy the parameters of the PTHcalcium relationship curve (PTHmin, PTHmaxsteady value, set point of calcium, slope of the curve, and PTHbasal/PTHmax ratio) were established for each patient according to the Felsenfeld definition [2]. Serum levels of IL-1, IL-6, TNF- and osteocalcin (BGP) were measured by ELISA. Plasma tartrate-resistant acid phosphatase (TRAP), a marker of osteoclastic activity, was measured by a colorimetric method. Group means were compared by Student's t test for dependent samples. Spearman correlation analysis was used to determine correlation between variables. Values for P of less than 0.05 were considered significant.
Results are shown in Table 1. Calcitriol administration led to a decrease in PTH basal, minimal, and maximal, PTHbasal/PTHmax ratio, as well as in serum TRAP, and to an increase in serum calcium and phosphorus. We found no significant influence of calcitriol on calcium set point, slope of the curve, or serum IL-1, IL-6 and TNF-
levels. Positive significant correlations were observed between IL-6 and pre-treatment values of PTHbasal (r=0.637 P=0.018), PTHmax (r=0.642 P=0.017), PTHmin (r=0.541 P=0.043), PTHbasal/PTHmax ratio (r=0.621 P=0.021), and TRAP (r=0.580 P=0.031). After calcitriol treatment, correlations between IL-6 and all other study parameters were no longer significant. TNF-
as well as IL-1 showed no significant correlations with any of the investigated parameters.
|
Furthermore, the lack of correlation between IL-6 and serum PTH, as well as TRAP values after calcitriol treatment, may result from the fact that PTH levels decreased after treatment. This is in agreement with the previous suggestion [6] that IL-6 may mediate bone resorption, particularly in cases of severe hyperparathyroidism.
References