Loss of alkaline phosphatase activity in duodenal mucosa: a marker for precursors of gastric metaplasia?

Biopsy specimens from duodenal mucosa in 34 patients with upper gastrointestinal symptoms and endoscopically abnormal mucosa (including duodenitis, active duodenal ulcer, and healed duodenal ulcer) and in 9 patients with histologically normal mucosa were examined histologically for gastric metaplasia and endogenous alkaline phosphatase (AP) activity. Using haematoxylin and eosin (H&E) and periodic acid-Schiff (PAS), we found gastric metaplasia in 91.2 per cent (31 out of 34) of patients with altered duodenal mucosa and in 33.3 per cent (3 out of 9) of patients with histologically normal, non-inflamed duodenal mucosa (P less than 0.001). To characterize gastric metaplasia further, histochemical methods for AP activity were applied to duodenal mucosa specimens. No AP activity was detected in complete metaplastic cells, but focal or diffuse loss of AP activity was frequently shown in otherwise normal appearing enterocytes next to metaplastic cell groups. Focal loss of AP activity was also detected in seven out of nine healthy controls (= 77.8 per cent) which appeared normal when stained with H&E. Our results suggest that the loss of AP activity in enterocytes may be an early marker of developing gastric metaplasia or at least a morphological manifestation of cell damage.