Peter R. Flanagan

Transferrin Receptors in the Human Gastrointestinal Tract Relationship to Body Iron Stores

Fluorescently labeled antibodies were used to identify transferrin receptors and mucosal transferrin in human gastrointestinal biopsy sections. Transferrin receptors were evident in the villous epithelium and the crypt areas of duodenum, ileum, and colon, predominantly in the basal-lateral area. In 7 subjects with low iron stores, the intensity of duodenal villous staining for receptor, on a scale of 0-4, was 2.1 +/- 0.3 (mean +/- SD). This value was significantly higher than the value in 13 subjects with normal iron stores (1.1 +/- 0.4). In 5 patients with hereditary hemochromatosis, duodenal transferrin receptor staining was not significantly different from that in the subjects with normal iron stores. Transferrin staining was found in the apical cytoplasm of epithelial cells in the duodenum, ileum, and colon, but observer assessment was not sufficiently reproducible to make a quantitative analysis. Our results suggest that iron deficiency is accompanied by an increase in transferrin receptors in duodenal absorptive cells, and the genetic lesion in hemochromatosis does not involve an increase in transferrin receptors in the intestinal mucosa compared with subjects with normal iron stores.

Diagnostic Efficacy of Hepatic Computed Tomography in the Detection of Body Iron Overload

To determine whether or not hepatic computed tomography density is an alternative to liver biopsy for the diagnosis of body iron overload, hepatic computed tomography density was determined in healthy controls, patients with idiopathic hemochromatosis, and patients with liver disease. Hepatic computed tomography density was obtained from a single computed tomography slice taken through the liver on a General Electric CT/T 8800 scanner. In 69 controls, hepatic computed tomography density ranged from 11 to 36 units (mean = 30). Given an upper limit of normal of 36 computed tomography units, 4 of 6 untreated patients with idiopathic hemochromatosis had elevated hepatic computed tomography density compared with 0 of 8 patients after venesection (X2 = 7.5, p = 0.01). Hepatic computed tomography density correlated directly with serum ferritin (r = 0.72, p = 0.01). In 58 consecutive patients with clinical or biochemical evidence, or both, of liver disease who underwent liver biopsy for diagnostic purposes, 0 of 52 patients with normal hepatic iron had an elevated hepatic computed tomography density as compared with 4 of 6 patients with excess iron (X2 = 35, p less than 0.001). An elevated hepatic computed tomography density associated with an elevated serum ferritin indicates iron overload; however, a normal hepatic computed tomography density does not exclude iron overload. When computerized tomography is applied to patients with an unexplained elevation of the serum ferritin, it provides a noninvasive alternative to liver biopsy for the detection of excess hepatocellular iron.

Measurement of dietary cadmium absorption in humans

Total body counting was used to determine cadmium absorption in 14 healthy subjects and in 1 patient with an ileostomy. Breakfast was extrinsically tagged with 115mCdCl2, and a poorly absorbed marker, 51CrCl3, was added to determine the point of complete elimination of unabsorbed radiocadmium from the gastrointestinal tract. The 51Cr was not an ideal marker: fecal excretion of radiocadmium continued beyond the point at which chromium was completely eliminated from the body, Nevertheless, it was helpful in six subjects in identifying the presence of unabsorbed radiocadmium still in transit in the lumen of the gastrointestinal tract 3--5 wk after the test meal. The average body retention of radiocadmium determined between 7 and 14 d after the disappearance of the chromium marker from the body was 4.6 +/- 4.0% (SD), with a range of 0.7--15.6%. The biological half-time of absorbed radiocadmium in one of the subjects was 100 d.

Interrelationships between iron and lead absorption in iron-deficient mice.

Mice were made iron-deficient by feeding a semisynthetic low-iron diet, by bleeding, or by a combination of both methods. Dietary-induced iron deficiency, by itself, enhanced iron absorption from an. intragastric dose to a much greater extent than did bleeding mice fed an iron-supplemented diet. Enhanced lead absorption was seen in the former but not in the latter group. Bleeding was effective, however, in raising lead absorption when mice were fed the iron-deficient diet. Additionally, the kinetics of lead absorption were studied by using an openended duodenal perfusion technique. When lead was perfused in solutions containing either 0.15 M sodium chloride or 0.15 M sodium ascorbate, irondeficient animals took up more lead into the mucosa and transferred more to the body than mice fed an iron-supplemented diet. Intestinal uptake of lead from both perfusates in iron-sufficient animals appeared to occur by a process that was primarily dependent on the luminal lead concentration. Lead uptake from the saline perfusate in iron-deficient mice was also directly related to the lead concentration of the perfusate, whereas uptake from the ascorbate perfusate was proportionally greater from lowerthan from higher-lead concentrations, giving rise to saturation-type kinetics. Lead transfer to the body from both types of perfusate also displayed saturation kinetics in both iron-sufficient and iron-deficient animals. When iron and lead were perfused together in 0.15 M sodium ascorbate, iron inhibited lead up take and transfer at Fe/Pb molar ratios as low as 0.5:1, whereas lead inhibited iron uptake and transfer at a Pb/Fe ratio of 5:1. These mutually inhibitory effects were not as easily demonstrated with a saline perfusate. Our results suggest that lead absorption occurs by two simultaneous processes: the first is a diffusion-type mechanism, and the second is a carrier-mediated process, which is enhanced by feeding a low-iron diet. Lead appeared to have less affinity than iron for the latter mechanism.

Zinc absorption and leukocyte zinc in alcoholic and nonalcoholic cirrhosis

To determine if malabsorption of zinc contributes to the zinc deficiency found in cirrhosis, the absorption of an oral dose of ZnCl2, labeled with65Zn and a nonabsorbed marker51CrCl3, was determined from the ratio of these isotopes in a stool specimen. Average65Zn absorption in 25 alcoholic cirrhotics, 37±17% (sd), was low compared to 55±16% in 31 healthy volunteer controls (P<0.01). In contrast, mean65Zn absorption, 47±11%, in 11 nonalcoholic cirrhotics was not significantly different from the average result in healthy controls. Low65Zn absorption was accompanied by low leukocyte zinc in a subgroup of alcoholic cirrhotics with ascites and/or ascites and encephalopathy, but not in the subgroup in which these clinical features were absent. Thus, low zinc absorption contributes to zinc deficiency in decompensated alcoholic cirrhosis. The failure to find similar abnormalities in nonalcoholic cirrhosis suggests that the long-standing consumption of alcoholic beverages contributes to the malabsorption of zinc.

Inhibition of iron absorption by omeprazole in rat model.

Since gastric acid is an important luminal factor in the absorption of non-heme iron, the effect of omeprazole on the absorption of iron in a rat model was studied. Iron absorption studies were performed on rats on a normal diet (N=42) and rats fed an iron-deficient diet (N=43) for three weeks. Rats were orally dosed with 40 μmol/kg of omeprazole or placebo daily for two days prior to iron absorption studies. Rats were orally dosed with 1 mmol of ferrous chloride, ferric chloride or food iron (dietary suspension) containing 11 μg of iron and labeled with 1 μCi of59Fe. Omeprazole-treated rats on the normal diet had no significant reduction in the absorption of ferric, ferrous, or food iron. In the rats on the iron-deficient diet, the absorption of ferrous iron decreased from 76±7.5% (mean±se) in control rats to 38±8.5% in the omeprazole-treated rats (P<0.003) and the absorption of food iron decreased from 65±7.5% in control rats to 37±6.5% in the omeprazole-treated rats (P<0.016). There was no significant reduction in the absorption of ferric iron. Omeprazole therapy is unlikely to be associated with significant iron malabsorption in normal patients but may reduce iron absorption in pathological states associated with increased iron absorption such as iron deficiency.

Abnormalities in iron metabolism in multiple sclerosis.

High iron concentrations have been reported in the brains of multiple sclerosis victims. To determine if there are abnormalities in general iron metabolism indicative of iron overload in MS, measurements of transferrin saturation, serum ferritin and red cell ferritin in 31 female and 18 male patients were compared to the results in 49 age- and sex-matched healthy controls. Compared to controls, mean serum ferritin in MS was high, whereas transferrin saturation and red cell ferritin were similar. High values in one or more individual test results were observed in eleven MS patients. They were prevalent in patients who required bilateral assistance to walk or were confined to a chair, and appeared to be related to the severity of the disease. An investigation was made into the relationship of the high serum ferritin values in MS to the HLA-A3 histocompatibility antigen, a marker of the hemochromatosis gene which is prevalent in MS. A statistically significant interaction was not found between serum ferritin and the presence of HLA-A3.

Zinc absorption in inflammatory bowel disease

Zinc absorption was measured in 29 patients with inflammatory bowel disease and a wide spectrum of disease activity to determine its relationship to disease activity, general nutritional state, and zinc status. Patients with severe disease requiring either supplementary oral or parenteral nutrition were excluded. The mean65ZnCl2 absorption, in the patients, determined using a65Zn and51Cr stool-counting test, 45±17% (SD), was significantly lower than the values, 54±16%, in 30 healthy controls,P<0.05. Low65ZnCl2 absorption was related to undernutrition, but not to disease activity in the absence of undernutrition or to zinc status estimated by leukocyte zinc measurements. Mean plasma zinc or leukocyte zinc concentration in patients did not differ significantly from controls, and only two patients with moderate disease had leukocyte zinc values below the 5th percentile of normal. In another group of nine patients with inflammatory bowel disease of mild-to-moderate severity and minimal nutritional impairment,65Zn absorption from an extrinsically labeled turkey test meal was 31±10% compared to 33±7% in 17 healthy controls,P>0.1. Thus, impairment in65ZnCl2 absorption in the patients selected for this study was only evident in undernourished persons with moderate or severe disease activity, but biochemical evidence of zinc deficiency was uncommon, and clinical features of zinc depletion were not encountered.

Zinc metabolism in patients on maintenance hemodialysis.

Recent studies have focused attention on the possible role of zinc depletion in the pathogenesis of uremic symptoms such as dysgeusia and impotence. The present studies were undertaken to evaluate the prevalence of zinc deficiency and abnormalities of zinc metabolism in patients with end-stage renal disease. A total of 43 stable chronic hemodialysis patients were screened for evidence of zinc deficiency by measurement of fasting predialysis leukocyte and plasma zinc. The results were compared with those from 30 healthy volunteers. Seventeen of these 43 patients had 65Zn absorption measured, and in 9 the rate of disappearance of 65Zn from the body was also measured. The results were compared with those obtained in 20 healthy controls. The nutritional status of these 17 patients was estimated by global nutritional assessment and calculation of the Quetelet index while 9 of 17 had dietary zinc intake calculated from a diet history. The mean plasma zinc level was lower in the hemodialysis patients (11.7 +/- 2.3 mumol/l vs. 13.3 +/- 2.9 mumol/l in controls; p less than 0.05). The mean leukocyte zinc level was 0.81 +/- 0.27 mumol/g dry weight in dialysis patients and 0.81 +/- 0.22 mumol/g in controls (p greater than 0.2). The mean 65Zn absorption in the patients was 49 +/- 14% and in controls 53 +/- 12% (p greater than 0.2). Mean turnover of body 65Zn was 0.47 +/- 0.11%/day in patients and 0.43 +/- 0.18%/day in controls (p greater than 0.1). The mean 65Zn half-life was 154 +/- 29 days in patients and 187 +/- 75 days in controls (p greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Mucosal iron in the control of iron absorption in a rat intestinal transplant model

Isogeneic intestinal transplantation of iron-loaded and iron-deficient intestine into iron-deficient rats was performed in 20 Lewis rats to isolate the effect of intestinal mucosal iron on iron absorption. Rats were iron loaded with three weekly IM injections of 50 mg of iron dextran and were rendered iron deficient with an iron-deficient diet for 3 weeks. Iron status was assessed by hepatic and gut mucosal iron determination. Uptake and transfer of 59Fe-ascorbate was measured in an isolated perfused segment of transplanted intestine 48 hours after transplantation. The mean rate of uptake of 59Fe from an iron-loaded intestine (mean mucosal iron concentration, 7.97 +/- 2.02 mumol/g) was 431 +/- 27 nmol/30 min, and from an iron-deficient intestine (mean mucosal iron concentration, 1.35 +/- .84 mumol/g), 743 +/- 222 nmol/30 min (P less than 0.001). The mean transfer of 59Fe from the mucosal cell to the body through an iron-loaded intestine was 63 +/- 22 nmol/30 min, and through an iron-deficient intestine was 86 +/- 32 nmol/30 min (P less than 0.05). These results suggest that the gut mucosal iron concentration regulates the uptake and transfer of iron in the intestine.