Abnormal arachidonic acid content of red blood cell membranes and main lithogenic factors in stone formers.

Increased arachidonic acid content in red blood cell membranes of stone formers (SF) has recently been reported and is hypothesized as representing the underlying causal factor for both hyperoxaluria and hypercalciuria. We performed the present study to see whether we could confirm this finding and to test whether any relationship exists between the fatty acid composition of red blood cell membranes and the main metabolic factors involved in stone formation. METHODS: In 21 SF and 40 healthy controls subjects the fatty acid composition of red blood cell membranes was assessed. In addition, the following parameters were evaluated in SF: daily and fasting urinary calcium excretion, fractional intestinal calcium absorption, 1,25-dihydroxy-vitamin D, intact parathyroid hormone, hydroxyproline in fasting urine, daily urinary excretion of oxalate, citrate, urate, electrolytes, urea, sulphate, relative supersaturation for calcium oxalate monohydrate. RESULTS: The red blood cell membrane of SF had a lower content of arachidonic acid, linoleic acid, and docosahexaenoic acid than that of control subjects. Arachidonic acid content was not correlated with any of the parameters studied. However, when patients were grouped according to the degree of oxalate excretion, hyperoxaluric SF had a higher arachidonic acid content and arachidonic/linoleic acid ratio than SF with normal oxalate excretion. CONCLUSIONS: Our results do not confirm the finding of an increased arachidonic acid content of red blood cell membrane in SF. On the contrary, reduced arachidonic acid levels were found in our patients. However, hyperoxaluric SF had a relatively higher arachidonic acid content than SF with normal urinary oxalate excretion.