Peter R. Holt

Enteropathy Associated with the Acquired Immunodeficiency Syndrome

To explore the effect of the acquired immunodeficiency syndrome on gastrointestinal structure and absorption, the cases of 12 homosexual men with the syndrome and 11 homosexual controls were studied. Seven patients had diarrhea with weight loss. Bacterial or parasitic infections were not detected. All patients were malnourished; had significantly fewer T-lymphocyte helper and suppressor cells; and had significantly lower body weights, midarm circumferences, serum albumin concentrations, and iron binding capacities than homosexual controls. D-Xylose malabsorption and steatorrhea were present in patients, especially those with diarrhea. Jejunal and rectal biopsy samples were histologically abnormal in all patients with diarrhea. Jejunal abnormalities included partial villus atrophy with crypt hyperplasia and increased numbers of intraepithelial lymphocytes. Rectal abnormalities included intranuclear viral inclusions, mast cell infiltration in the lamina propria, and focal cell degeneration near the crypt base. The histologic findings suggest that a specific pathologic process occurs in the lamina propria of the small intestine and colon in some patients with the syndrome.

Lovastatin augments sulindac-induced apoptosis in colon cancer cells and potentiates chemopreventive effects of sulindac

BACKGROUND & AIMS 3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors (HRIs) were found incidentally to reduce new cases of colon cancer in 2 large clinical trials evaluating coronary events, although most patients in both treatment and control group were taking nonsteroidal anti-inflammatory drugs (NSAIDs). NSAIDs are associated with reduced colon cancer incidence, predominantly by increasing apoptosis. We showed previously that lovastatin induces apoptosis in colon cancer cells. In the present study we evaluated the potential of combining lovastatin with sulindac for colon cancer chemoprevention. RESULTS Lovastatin, 10-30 micromol/L, augmented sulindac-induced apoptosis up to 5-fold in 3 colon cancer cell lines. This was prevented by mevalonate (100 micromol/L) or geranylgeranylpyrophosphate (10 micromol/L) but not farnesylpyrophosphate (100 micromol/L), suggesting inhibition of geranylgeranylation of target protein(s) as the predominant mechanism. In an azoxymethane rat model of chemical-induced carcinogenesis, the total number of colonic aberrant crypt foci per animal (control, 161 +/- 11) and the number of foci with 4+ crypts (control, 40 +/- 4.5) decreased to 142 +/- 14 (NS) and 43 +/- 2.9 (NS), respectively, with 50 ppm lovastatin alone; to 137 +/- 5.4 (P = 0.053) and 36 +/- 2.1 (NS) with 80 ppm sulindac alone; and to 116 +/- 8.1 (P = 0.004) and 28 +/- 3.4 (P = 0.02) when 50 ppm lovastatin and 80 ppm sulindac were combined. CONCLUSIONS Addition of an HRI such as lovastatin may augment chemopreventive effects of NSAIDs or/and may allow lower, less toxic doses of these drugs to be used.

Lipolysis and Absorption of Fat in the Rat Stomach

The triglyceride lipolytic activity of gastric mucosal homogenates was studied in Wistar strain rats with exclusion of pancreatic enzyme contamination by prior prolonged pancreatic flow diversion. Considerable hydrolysis of a medium chain triglyceride, trioctanoin, occurred, but enzyme activity using triolein as substrate was barely detectable. Although the pH optimum for lipolytic activity was 6.5, significant hydrolysis occurred at pH 3.5 and the enzyme was very stable at this low pH. Taurocholate at concentration of 2 to 20 mm did not alter the rate of lipolysis. In pyloric ligated rats in vivo, considerable hydrolysis of both trioctanoin and triolein was measured when the pH was as low as 2. In addition, absorption of octanoic acid from the gastric lumen was readily detectable. Gastric lipolytic activity may be important in the digestion of fat, particularly of medium chain length, both in the stomach and in the intestinal lumen in patients with pancreatic exocrine insufficiency and steatorrhea.

Ultrastructural abnormalities in Whipple's disease.

Summary A fasting jejunal biopsy specimen, obtained from a patient with Whipples disease, was studied by light and electron microscopic technics. Periodic acid-Schiff positive inclusions in the macrophages were found to have a complex ultrastructure consisting of a series of membranes, vesicles and granules. Dense bodies of unknown nature were observed in close approximation to the macrophage cell border, and within its substance. The virus-like character of these particles has been discussed.

Rate-limiting steps in steady-state intestinal absorption of trioctanoin-1-14C. Effect of biliary and pancreatic flow diversion.

During continuous intraduodenal infusion of emulsified fat in rats, a steady state of intestinal absorption is achieved. Maximal steady-state absorption of trioctanoin, a medium-chain triglyceride (MCT), by unanesthetized, restrained rats was found to be the same after total bile diversion as in controls (1560 mumoles of fatty acid per hr).After pancreatic and bile diversion, absorption of MCT was still one-third as rapid as in controls, and mucosal uptake apparently occurred in the form of unhydrolyzed triglyceride. Returning bile to the intestinal lumen during pancreatic diversion did not increase the absorption rate.From intestinal tissue lipid-(14)C concentrations measured during steady-state maximal absorption it was possible to calculate turnover times for labeled lipid passing through the mucosal cells. Mucosal turnover times of about 4 min for control and bile-diverted rats, and about 20 min for animals with pancreatic diversion were obtained. The rate-limiting step in octanoic acid absorption in control and bile-diverted rats was probably mucosal penetration. During absorption of unhydrolyzed triglyceride by pancreatic flow-diverted rats, both passage from the lumen into the mucosal cell and intracellular lipolysis were rate-controlling factors.

A Simple Method for Determining Epithelial Cell Turnover in Small Intestine: Studies in Young and Aging Rat Gut

Epithelial cell migration in animal gut classically is measured by autoradiography after systemic administration of tritiated thymidine. A migration rate is calculated from observations of the leading edge of villus epithelial cells containing labeled nuclei at varying time periods after tritiated thymidine injection. This method is very accurate, but laborious, time consuming, and costly. A new, simplified method for measuring epithelial cell measurement of [3H] deoxyribonucleic acid specific activity in frozen sections of intestine cryostat-cut from villus tip to crypt base. The leading edge of [3H]deoxyribonucleic acid can be detected reproducibly (coefficient of variation 11.25%). Autoradiographic and chemical methods for determining the leading edge of labeled cells compared favorable (r=0.848). Epithelial cell migration rates in barrier-reared Fisher 344 aging (27 mo) and young control (4-5 mo) rats were compared and no differences were detected in duodenum, jejunum, or ileum. Labeled epithelial cells reached the villus tip sooner in the ileum than in duodenum or jejunum. However, crypt-villus column heights were greater in duodenum and jejunum and the calculated epithelial cell migration rate was faster in upper intestine than in the ileum. Although ileal epithelial cells are shed from the villus sooner than cells in the upper intestine, the rate of cell migration in ileum is slower.

Use of 125-I- and 51-Cr-labeled albumin for the measurement of gastrointestinal and total albumin catabolism.

A method for the simultaneous measurement of gastrointestinal protein loss and total albumin turnover entailing the use of a combination of (125)iodine- and (51)chromium-labeled albumin is described. Albumin turnover was calculated by the measurement of albumin-(125)I plasma decay and cumulative urinary excretion, and the results obtained agreed closely with previous studies utilizing albumin-(131)I. Gastrointestinal catabolism was calculated from the rate of fecal excretion of (51)Cr and the specific activity of plasma albumin-(51)Cr, and these data were related to the calculated albumin turnover results. During the period of 6-14 days after administration, the ratio of specific activties of albumin-(125)I and -(51)Cr in plasma and in extravascular spaces or gastric and biliary secretions remained almost identical. Fecal excretion of (51)Cr was also quite stable at this time. In six normal subjects gastrointestinal catabolism accounted for less than 10% of total albumin catabolism. Excessive gastrointestinal protein losses did not contribute to the low serum albumin in three patients with cirrhosis or in two adults with the nephrotic syndrome. Multiple mechanisms leading to hypoalbuminemia were demonstrated in other subjects with a variety of gastrointestinal disorders.

Serum Alcohol Dehydrogenase, an Indicator of Intrahepatic Cholestasis

Abstract The activity of alcohol dehydrogenase, an enzyme present principally in liver tissue, was repetitively determined in the serums of 266 patients with hepatic and nonhepatic diseases. The enzyme was present only in patients with liver-cell necrosis. The level of serum activity reflected the extent of parenchymal necrosis, and in acute hepatitis the enzyme was present for as long as three weeks after onset of jaundice. Disappearance from the serum correlated with relief of intrahepatic cholestasis. In patients with hepatocellular necrosis and prolonged cholestasis persistent serum alcohol dehydrogenase activity was present while serum glutamic oxalacetic transaminase values fell close to normal. Only three of 40 patients with jaundice secondary to extrahepatic biliary obstruction had serum alcohol dehydrogenase elevation. These results indicate that serum activity is a specific reflection of hepatocellular necrosis, a good index of intrahepatic cholestasis and of value in the differential diagnosis ...

Inhibition of steady-state intestinal absorption of long-chain triglyceride by medium-chain triglyceride in the unanesthetized rat

Maximal steady-state intestinal absorption rates in unanesthetized rats for triolein, a long-chain triglyceride, and for trioctanoin, a medium-chain triglyceride, are known to differ. Both these lipids are hydrolyzed in the intestinal lumen but the products of hydrolysis are metabolized differently by the mucosal cell. Intraduodenal infusion of trioctanoin was found to reduce steady-state triolein absorption. Luminal lipolysis was shown not to be rate-controlling. High rates of trioctanoin infusion significantly lowered the pH of the luminal aqueous phase and altered the partition of oleic acid between aqueous and oil phases. Two possible mechanisms for the inhibition of triolein uptake are considered. In the intestinal lumen medium chain lipids might have lowered the activity of oleic acid monomers in the aqueous phase and reduced passive diffusion into mucosal cells. Alternatively, competition between long and medium chain fatty acids for some common receptor during transport into the intestinal mucosal cell may have occurred. Despite significant inhibition of triolein absorption by high levels of trioctanoin, the maximum number of calories absorbed from mixtures of triglycerides exceeded the maxima from either glyceride alone. The optimum proportion of triolein to trioctanoin in lipid infusion mixtures was about 3:4 by weight and the optimum dosages about half maximal for each triglyceride, which represented a caloric intake of 4 kcal/rat per 2 hr. The absorption coefficient for this lipid mixture was about 90%. It is suggested that in patients who have a limited intestinal absorptive capacity dietary fat intake might be doubled with a caloric supplement of medium-chain triglycerides without increase in steatorrhea of long-chain fat.

EFFECTS OF BILE SALTS ON GLUCOSE METABOLISM BY SLICES OF HAMSTER SMALL INTESTINE

Bile salts are known to be essential for the effective absorption of fat from the intestinal tract (1). They have been shown to stimulate the action of pancreatic lipase (2) and have an important emulsifying action on water-insoluble dietary triglycerides that is probably related to their ability to form micelles with fatty acids and monoglycerides (3). In addition to their role in triglyceride absorption, bile salts also appear to be essential in the absorption and esterification of vitamin A (4) and cholesterol (5). In previous studies from this laboratory (6), it was shown that conjugated bile salts enhanced the esterification of palmitate-C14 to triglycerides and appeared to stimulate the incorporation of glucose-C14 into glyceride-glycerol. These observations suggested that in the intestinal mucosa, bile salts influence the metabolism not only of lipid, but also of carbohydrate. The present experiments were designed to investigate further the actions of conjugated and unconjugated bile salts on glucose metabolism. These studies have been carried out with slices of hamster small intestine. In addition, because of some disagreement in the literature concerning the utilization of glycerol in the intestine (7, 8), the metabolism of glucose and glycerol by hamster intestinal mucosa has been compared.