William D. Heizer

Sulfite oxidase deficiency: Studies of a patient with mental retardation, dislocated ocular lenses, and abnormal urinary excretion of S-sulfo-l-cysteine, sulfite, and thiosulfate

Abstract This paper constitutes the first description of a previously unreported disorder of metabolism of sulfur-containing compounds. The patient was born with neurological abnormalities and deteriorated to a virtually decorticate state by nine months. Bilateral ectopia lentis was discovered at 1 year. We studied him at age 30 months and found his urine to contain abnormally increased amounts of S-sulfo- l -cysteine, sulfite, and thiosulfate. His urinary excretion of inorganic sulfate was markedly reduced and, in contrast to normal controls, it did not increase after administration of l -cysteine. These chemical abnormalities are best explained by the presence of a block in the conversion of sulfite to sulfate secondary to a deficiency of sulfite oxidase activity. Studies from tissues obtained from the patient postmortem reveal such a defect (5). The pathology could have been caused by toxic effects of accumulation of sulfite or perhaps other metabolites. Possibly, deficiency of inorganic sulfate could also have caused pathological changes. Although three of the patients seven siblings died in infancy with neurological disease, the remaining siblings and the parents do not bear clinical stigmata suggestive of the patients disease, and as yet we have detected no chemical abnormalities to suggest they are carriers of a trait. Thus, we suspect, but have no definite evidence, that the disease is an hereditary disorder of metabolism. We have named it sulfite oxidase deficiency.

In vitro-in vivo correlation of hepatobiliary drug clearance in humans.

The biliary clearance (Clbiliary) of three compounds was estimated using sandwich‐cultured human hepatocytes (SCHH) and compared with Clbiliary values measured in vivo. Tc‐99m sestamibi (MIBI) Clbiliary was determined in seven healthy volunteers using an oroenteric catheter to aspirate duodenal secretions, and gamma scintigraphy to determine gallbladder contraction; this technique was used previously to determine Tc‐99m mebrofenin (MEB) and piperacillin (PIP) in vivo Clbiliary. In vitro Clbiliary of MEB, MIBI, and PIP was quantified in SCHH as the ratio of mass excreted into bile canaliculi and area under the blood concentration‐time curve (AUC) in medium. MIBI Clbiliary in vivo was 5.5±1.2 mL/min/kg (mean±SD). The rank order of Clbiliary predicted from SCHH corresponded well with the in vivo Clbiliary values in mL/min/kg for MEB (7.44 vs 16.1), MIBI (1.20 vs 5.51), and PIP (0.028 vs 0.032). In conclusion, the methods developed allowed for reproducible quantification of Clbiliary of drugs in healthy humans and prediction of Clbiliary from in vitro data.

Efficacy of metoclopramide as an adjunct to duodenal placement of small-bore feeding tubes: a randomized, placebo-controlled, double-blind study:

We examined whether metoclopramide would improve the success rate of transpyloric intubation of a weighted Corpak feeding tube when fluoroscopic guidance is not used. Seventy patients were randomized in a prospective, double-blind fashion to receive either placebo (n = 35) or metoclopramide, 10 mg (n = 35) parenterally, administered immediately after the feeding tube was inserted. Tube location was determined independently by two observers who examined radiographs obtained after barium was instilled via the tube. There was no significant increase in the success rate of duodenal intubation in the total group following metoclopramide, 60%, compared to placebo, 49%. However, analysis of subgroups among the placebo-treated patients revealed that diabetes mellitus, but not other medical conditions, decreased the success rate for duodenal intubation, 20 vs 60% (p less than 0.05). Among diabetic patients, metoclopramide resulted in a significant increase in duodenal placement compared to placebo (p less than 0.05). We conclude that parenteral metoclopramide significantly increases the frequency of transpyloric intubation with small feeding tubes without fluoroscopic guidance in diabetic patients but not in nondiabetic patients.

Peptide hydrolase activities of the mucosa of human small intestine

Few studies have been published on peptide hydrolase activities of human small intestine mucosa. We developed methods to screen tissue extracts for such enzymes and to quantitate hydrolase activities for dipeptides containing the aromatic amino acid L-phenylalanine. The screening procedure indicated glycyl-L-proline hydrolase activity was reduced in biopsy specimens from patients with flattened intestinal mucosa. To explore this further, we established optimal assay conditions for hydrolase activities (a) glycyl-L-proline, (b) L-phenylalanyl-L-proline, (c) L-alanyl-L-phenylalanine, and (d) L-phenylalanylglycine. Biopsy specimens from patients with various intestinal disorders, but without flattened mucosa, and from three patients with flattened mucosa, showed a disproportionate reduction in activities (a) and (b), with the reduction being significantly more marked in the latter patients. We suggest that intestinal imidopeptide hydrolase activities, such as (a) and (b), are sensitive to changes in intestinal disease generally, particularly to the altered physiology associated with flattening of the mucosa, and are secondary to, rather than a cause of, the intestinal pathology. Our finding that intestinal alkaline phosphatase activity tended to parallel imidopeptide hydrolase activity, and that activity (a) was partially localized to the particulate fraction of mucosal homogenate, suggested that imidopeptide hydrolase activities may be located in the microvilli of the intestinal epithelium and that, like alkaline phosphatase activity, they may be reduced in flattened mucosae, in part at least because of the pathologic changes in the microvilli. In our studies of control subjects we did not detect peptide hydrolase activity deficiency analogous to asymptomatic disaccharidase deficiency.

Influence of Gastrointestinal Site of Drug Delivery on the Absorption Characteristics of Ranitidine

The absorption characteristics of ranitidine after delivery to three locations in the gastrointestinal tract were compared in an open-label study of eight healthy males. Subjects received ranitidine HCl (150 mg) for injection via a nasoenteric tube directly into their stomach, jejunum, or cecum sequentially in three separate periods (24 hr apart). Plasma samples were collected at periodic time intervals for 12 hr following each dosing and analyzed for ranitidine concentration by high-pressure liquid chromatography. Mean concentrations following cecal dosing were lower (P < 0.05) than concentrations following gastric or jejunal dosing at each sampling time except baseline. Mean concentrations following gastric and jejunal dosing were similar except at 2 hr (gastric > jejunal). Mean pharmacokinetic parameters for cecal administration were different (P < 0.05) from either the gastric or the jejunal periods with the exception of Tmax. There was no difference in any pharmacokinetic parameter after gastric or jejunal dosing. The relative bioavailability after cecal administration was less than 15% of that observed after administration into the stomach or jejunum. Additionally, Wagner-Nelson analysis indicated that the rate of ranitidine absorption was much slower following cecal administration than after gastric or jejunal dosing. Two plasma concentration peaks were observed in three of eight subjects after gastric dosing, in eight of eight subjects after jejunal dosing, and in zero of eight subjects after cecal dosing. These data demonstrate that the absorption profile of ranitidine is equivalent, in extent and duration, after delivery to the stomach or jejunum, while absorption from the cecum is significantly less. In addition, the two plasma concentration peaks commonly seen with ranitidine administration are not secondary to variations in gastric emptying as has been hypothesized.

Efficacy of Tube Feeding in Supplying Energy Requirements of Hospitalized Patients

During a 6-week period, all adult patients in a university hospital receiving ready-to-feed nasoenteric tube feeding formula were prospectively studied. The study objective was to determine each patients caloric intake from tube feeding relative to their energy needs and to identify factors causing decreased feeding intake. Each of 35 patients was visited at least once daily to determine their volumetric intake of tube feeding formula. Daily review of patient care records and nursing interviews were used to identify interruptions in therapy. Patients basal energy expenditures (BEE) were calculated using the Harris-Benedict equation. Calorie goals were set by members of the Nutrition Support Service or clinical dietitians. Intakes averaged 1095 +/- 41 Kcal (SEM) per day or 61% of their mean calorie goal of 1791 +/- 41 Kcal. Mean daily calorie intake was statistically different (p less than 0.05) from mean energy goal on patient study days 1 through 5, 7, and 8. Only 16 of the 35 patients achieved an intake of 100% of their energy goal on any day of therapy. Calorie goals averaged 1.4 times BEE. Mean daily calorie intake did not exceed BEE until study day 10. Eighteen % of potential feeding time was lost due to temporary feeding interruptions; primarily inadvertent extubation (4.6%), gastrointestinal intolerance (4.7%), medical procedures requiring discontinuation of feeding (2.8%), and feeding tube positioning difficulties (1.5%). In addition, physicians ordered only 75% of calculated energy goals. These data indicate that tube feeding therapy, when provided under usual hospital conditions, does not meet patients energy requirements.

Intestinal Effects of Sulfate in Drinking Water on Normal Human Subjects

Uncontrolled observations implicate sulfate indrinking water at concentrations exceeding 500-700mg/liter as a cause of diarrhea, but controlled studieshave not been reported. We conducted a controlled study in normal adults to determine the effectof various drinking water sodium sulfate concentrationson bowel function. Ten healthy subjects were given aconstant diet and fluid intake. Fluid consisted of 36 ml/kg/day of drinking water of variousknown sulfate concentrations and 500 ml of other fluid.In a dose-ranging study, four subjects received drinkingwater with sulfate concentrations of 0, 400, 600, 800, 1000, and 1200 mg/liters for sixconsecutive two-day periods. In a single-dose study, sixother subjects received water with sulfateconcentrations of 0 and 1200 mg/liter for twoconsecutive six-day periods. Stool mass, frequency, and consistencyand mouth-to-anus appearance time of colored markerswere measured. In the dose-ranging study, the onlysignificant linear trend was decreasing mouth-to-anus appearance time with increasing sulfateconcentrations. In the single-dose study, 1200 mg/litersulfate caused a significant but clinically mildincrease in mean stool mass per six-day pool from 621 gto 922 g (P = 0.03). When all 10 subjects wereused to compare effects of 0 mg/liter and 1200 mg/litersulfate, significant differences in stool consistency (P= 0.02) and transit time (P = 0.03) were observed. None of the subjects reported diarrhea orpassed more than three stools per day. In 10 normaladult subjects, sulfate in drinking water at aconcentration of 1200 mg/liter, which is higher thanreported to occur in US municipal water sources, causeda measurable but clinically insignificant increase instool mass and decrease in stool consistency andappearance time, but no change in stool frequency and no complaint of diarrhea.

Human Intestinal Brush Border Peptidases

Hydrolysis of small peptides, like disaccharide hydrolysis, is an important function of the intestinal brush border, but little is known of the individual human peptidases. The purposes of this study were to detect all human brush border enzymes hydrolyzing dipeptides and tripeptides, identify the most discriminating substrate for each enzyme in order to permit assays in crude mixtures, and begin biochemical characterization of each enzyme. Four brush border peptidases were identified. Enzymes I (aspartate aminopeptidase, E.C. 3.4.11.7) and III (amino-oligopeptidase, E.C. 3.4.11.2) are known brush border enzymes. Enzymes II (membrane Gly-Leu peptidase) and IV (zinc stable Asp-Lys peptidase) have not been identified in human brush border previously. They are distinct from dipeptidyl aminopeptidase IV, carboxypeptidase, and gamma-glutamyl transferase. The substrate most discriminating for each enzyme is alpha-Glu-beta-naphthylamide for I (100% of the brush border activity for this substrate is due to enzyme I), glycylleucine for II (80%), leucyl-beta-naphthylamide for III (91%), and aspartyl-lysine in 5 mM Zn2+ for IV (63%). The enzymes are immunologically distinct and antibodies to each one localize to the brush border on immunohistochemical staining. Purification of 142-, 79-, 158-, and 46-fold was achieved for enzymes I through IV, respectively. Biochemical characteristics include slightly alkaline pH optima, molecular weights of 91,000-190,000, and evidence of metal ion involvement in activity. These studies provide necessary information for determining the role of brush border peptidase deficiencies in human disease.

A novel method for the determination of biliary clearance in humans

Biliary excretion is an important route of elimination and the biliary tract is a potential site of toxicity for many drugs and xenobiotics. Quantification of biliary excretion in healthy human volunteers is logistically challenging and is rarely defined during drug development. The current study uses a novel oroenteric tube coupled with a specialized clinical protocol to examine the pharmacokinetics of99mTechnetium (Tc-99m) mebrofenin, a compound that undergoes rapid hepatic uptake and extensive biliary excretion. A custommade multilumen oroenteric tube was positioned in the duodenum of healthy human volunteers. Subjects were positioned under a gamma camera and 2.5 mCi of Tc-99m mebrofenin was administered intravenously. Duodenal aspirates, blood samples, and urine were collected periodically for 3 hours. Two hours after Tc-99m mebrofenin administration, the gallbladder was contracted with an intravenous infusion of cholecystokinin-8. Gamma scintigraphy was used to determine the gallbladder ejection fraction in each subject. Total systemic clearance of Tc-99m mebrofenin approximated liver blood flow (Cltotal 17.3±1.7 mL/min/kg), and 35% to 84% of the Tc-99m mebrofenin dose was recovered in bile. However, when the data were corrected for the gallbladder ejection fraction, 71% to 92% of theexcreted Tc-99m mebrofenin dose was recovered. This novel croenteric tube and clinical protocol provide a useful method to quantify biliary excretion of xenobiotics in healthy human volunteers.

Parenteral nutrition at home for 5 years via arteriovenous fistulae. Supplemental intravenous feedings for a patient with severe short bowel syndrome

On March 26, 1970, a 33-year-old male suffered intestinal infarction which required total enterectomy and duodeno-transverse colostomy. Nutrition was maintained in the hospital by daily parenteral feeding for 2 months postoperatively, after which parenteral feedings were decreased and stopped for long periods. Various oral dietary regimens failed to provide adequate nutrition, and the patient lost 40 kg and became severely malnourished during the next 13 months. In June 1971, supplemental home parenteral nutrition (PN) via an arteriovenous fistula was instituted on a 3 or 4 nights per week basis. The patients weight and strength increased markedly after institution of the home supplemental PN program. The first fistula became occluded after 9.5 months of home PN use and subsequent successive fistulae have remained patent for 31.3, 8.8, and 5.5 months of use. The patient prepares his own PN fluids at home, using a commercial device for filling plastic intravenous fluid bags. Although several different types of fluid have been used, the current mixture of 25% glucose and 2.75% amino acids with added vitamins, potassium, calcium, magnesium, and insulin plus simultaneously administered lipid emulsion has proven most effective. Only when the patients low fat, low oxalate diet is supplemented with this parenteral mixture 4 nights each week is he in positive nitrogen, phosphorus, and magnesium balance. However, his negative calcium balance is only partially corrected. There has been no sepsis, embolism, or fistula infection during 5 years of home PN.