Chemotherapy for cancer causes apoptosis that precedes hypoplasia in crypts of the small intestine in humans

BACKGROUND AND AIMS

The mechanism of gastrointestinal damage (mucositis) induced by cancer chemotherapy remains uncertain. The aims of this study were to define the time course and mechanism of small intestinal damage following chemotherapy in humans.

METHODS

Patients receiving chemotherapy underwent upper gastrointestinal endoscopy (a maximum of two per patient) with duodenal biopsy prior to chemotherapy and again at 1, 3, 5, and 16 days after chemotherapy. Tissue was taken for morphometry, disaccharidase assays, electron microscopy, and for assessment of apoptosis using the Tdt mediated dUTP-biotin nick end labelling (TUNEL) method. Villus area, crypt length, and mitotic index were measured by a microdissection technique.

RESULTS

Apoptosis increased sevenfold in intestinal crypts at one day, and villus area, crypt length, mitotic count per crypt, and enterocyte height decreased at three days after chemotherapy. Disaccharidase activities remained unchanged. Electron microscopy showed increased open tight junctions of enterocytes at day 3, consistent with more immature cells. All indices improved by 16 days.

CONCLUSION

Small intestinal mucositis is associated with apoptosis in crypts that precedes hypoplastic villous atrophy and loss of enterocyte height.

Zinc deficiency is associated with suppression of colonocyte proliferation in the distal large bowel of rats

As zinc status may influence susceptibility to colon cancer, we examined the effect of dietary zinc deficiency on the proliferation of epithelial cells (colonocytes) in the large bowel of rats. When compared to feed-restricted rats, those with zinc deficiency showed a significant reduction in proliferation in the distal colon as assessed by accumulated metaphase arrest and crypt cell production rates in vivo. Zinc deficiency had no apparent effect on thymidine kinase activity in colonocytes but was accompanied by minor changes in fecal mass and fecal pH. In rats, zinc deficiency is associated with a reduction in the rate of proliferation of colonocytes in the distal colon.

Proliferative activity in the proximal and distal colon of the rat after fasting and refeeding

Several methods were used to assess proliferation of colonocytes in the proximal and distal colon of the rat after fasting and refeeding. Those applied in vivo included metaphase arrest, labelling with bromodeoxyuridine and uptake of tritiated thymidine. The latter two techniques were also applied after isolation of colonocytes in vitro. Methods applied in vivo showed similar proliferation in the proximal and distal colon after fasting and enhanced proliferation in both regions after refeeding. However, the degree of enhancement was greater in the distal colon than in the proximal colon. In vitro, proliferation was enhanced in both the proximal and distal colon after refeeding but the degree of variability was greater than after assessment in vivo. Methods applied in vivo are preferred for assessment of proliferative activity in the rat colon, and major changes in proliferation in both proximal and distal colon can be induced by fasting-refeeding.

Renal potassium adaptation in the rat: role of glucocorticoids and aldosterone

This study examines the role of adrenocortical hormones in the kaliuresis following an acute intragastric KCl load in conscious control (CK) and high potassium diet (HK) rats. Adrenalectomy, 1 day before test, reduced K+ excretion by 35% in CK and 60% in HK rats, leading to minimal differences in K excretion between CK and HK. By contrast, spironolactone inhibited K excretion by only 10%. Glucocorticoids (dexamethasone 3-10 micrograms/100 g) increased K+ excretion in adrenalectomized CK and to a greater extent in adrenalectomized HK rats. Aldosterone (3 micrograms/100 g) alone had a variable effect on urinary potassium excretion in adrenalectomized rats. A combination of dexamethasone (3 micrograms/100 g) and aldosterone (3 micrograms/100 g) in adrenalectomized rats induced potassium excretion equivalent to that in intact rats. Adrenalectomized HK rats had a greater kaliuretic response to dexamethasone and aldosterone than CK rats. These results 1) demonstrate a role for glucocorticoids in K+ excretion in HK rats and 2) illustrate the importance of the increased responsiveness to both glucocorticoids and mineralocorticoids in potassium adaptation.

Cyproheptadine and mineralocorticoid effector mechanisms

Cyproheptadine has recently been reported to blunt the furosemide-induced rise in PRA in normal subjects and to acutely lower plasma aldosterone levels in patients with hyperaldosteronism due to bilateral adrenal hyperplasia; both actions have tentatively been ascribed to the antiserotoninergic action of the drug. We here describe receptor studies showing cyproheptadine to occupy mineralocorticoid, but not glucocorticoid, receptors in rat and mouse kidney. On bioassay, cyproheptadine is a partial mineralocorticoid agonist/predominant antagonist.