Howard G. Parsons

Plasma L-arginine concentrations in premature infants with necrotizing enterocolitis

OBJECTIVE To determine whether L-arginine concentrations (the substrate for nitric oxide synthesis) are lower in premature infants in whom necrotizing enterocolitis (NEC) develops than in unaffected infants. METHODS We measured arginine and nutritional intake, plasma arginine, glutamine, total amino acids, and ammonia concentrations in 53 premature infants (mean gestational age +/- SD: 27 +/- 1.7 weeks) at risk of NEC. Measurements were done on days 3, 7, 14 and 21 and just before treatment in infants with NEC. RESULTS Necrotizing enterocolitis developed in 11 infants between postnatal days 1 and 26. On day 3, plasma arginine concentrations were decreased compared with normal published values (mean +/- SE, 41 mumol/L +/- 4). Arginine concentrations increased with day of life of measurement (p < 0.001) and arginine intake (p < 0.001). Plasma arginine concentrations were significantly lower at the time of diagnosis in infants with NEC compared with control subjects, even after adjusting for arginine intake and day of life (p = 0.032). Plasma glutamine and total amino acid concentrations were not significantly different in infants with NEC compared with control subjects. Plasma ammonia concentrations were elevated on day 3 (mean +/- SE, 72 +/- 3.3 mumol/L) and decreased with postnatal age (p < 0.001) and increasing plasma arginine concentrations (p < 0.001). CONCLUSION Plasma arginine concentrations are decreased at the time of diagnosis in premature infants with NEC. The potential benefit of arginine supplementation in the prevention of the disease deserves evaluation.

The T-786→C Mutation in Endothelial Nitric Oxide Synthase Is Associated With Hypertension

Although the pathogenic mechanisms involved in predisposing individuals to hypertension are not well defined, evidence is accumulating that suggests a strong genetic transmission. Animal studies and some clinical investigations have revealed that aberrant NO production may be an important contributing factor. Indeed, a missense mutation in the endothelial NO gene caused by a Glu298Asp alteration has been strongly associated with essential hypertension, coronary artery spasm, and myocardial infarction. Recently, another point mutation caused by a T-786→C transition in the 5′-flanking region of the endothelial NO synthase gene has been identified and, like the Glu298Asp mutation, is associated with coronary artery spasm. The present study was conducted to determine the effect of the T-786→C point mutation on hypertension. We investigated the interaction between the endothelial NO synthase T-786→C polymorphism and blood pressure in a large (n=705) clinically healthy population. Allele frequencies for the T and C alleles were 62% and 38%, translating into 39%, 46% and 15% of the population having the T/T, T/C, and C/C genotypes, respectively, for the T-786→C point mutation. Subjects with the C/C genotype had significantly higher systolic blood pressures and were 2.16(95% confidence interval, 1.3 to 3.7) more likely to be hypertensive. Therefore, the −786 C/C genotype in NO synthase is a significant contributing factor for increasing the risk of essential hypertension.

Hyperhomocyst(e)inemia and the prevalence of atherosclerotic vascular disease in patients with end-stage renal disease

Hyperhomocyst(e)inemia is now recognized as an independent risk factor for atherosclerotic cardiovascular disease in patients with normal renal function. Hyperhomocyst(e)inemia is common in patients with chronic renal failure. This study is designed to look for an association between hyperhomocyst(e)inemia and atherosclerotic vascular disease in patients with end-stage renal disease (ESRD). Two hundred eighteen patients undergoing hemodialysis were enrolled onto the study and had predialysis bloodwork performed for total homocyst(e)ine, red blood cell folate, and vitamin B(12) levels. A history of clinically significant atherosclerotic vascular disease (ischemic heart disease, cerebrovascular disease, or peripheral vascular disease) was elicited by patient questionnaire and verified by careful inpatient and outpatient chart review. Atherosclerotic vascular disease was present in 45.9% of patients. Mean homocyst(e)ine concentration was 26.7 micromol/L (95% confidence interval [CI], 25.0 to 28.4) overall. Mean homocyst(e)ine concentration was 28.6 micromol/L (95% CI, 25.6 to 31.7) and 25.0 micromol/L (95% CI, 23.2 to 26.8) in patients with and without atherosclerotic disease, respectively (P = 0.036). The adjusted odds ratio for atherosclerotic disease was 2.12 (95% CI, 1.03 to 4.39) for those subjects with a homocyst(e)ine level in the highest quartile compared with the lowest 3 quartiles. In the 126 men, the adjusted odds ratio for atherosclerotic disease was 3.4 (95% CI, 1. 24 to 9.42) for those with homocyst(e)ine levels in the highest quartile compared with the lowest 3 quartiles. No association was found between homocyst(e)ine level and atherosclerotic disease in women. In conclusion, there is an association between hyperhomocyst(e)inemia and atherosclerotic vascular disease in patients undergoing dialysis. Prospective studies need to further examine the relationship between homocyst(e)ine level and atherosclerosis in women with ESRD.

Effect of heterozygosity for the methionine synthase 2756 A→G mutation on the risk for recurrent cardiovascular events

Increased dietary intake of folate has been shown to significantly reduce the risk for fatal myocardial infarction, possibly by lowering homocysteine levels. We therefore investigated the association between recurrent cardiovascular events and a mutation in methionine synthase (2756 A-->G)--an enzyme directly involved in folate and homocysteine metabolism. This mutation significantly reduced the risk for recurrent cardiovascular events and elevated red blood cell folate levels.

Effects of Medium-Chain Triglyceride Feeding on Energy Balance in Adult Humans

In recent years, the metabolism of triglycerides has attracted much attention. Oxidation of fatty acids is an essential energy supply, especially when glucose supply is limited. In the present study, the effect of a 3-day high medium-chain triglyceride (MCT; 51% of calories), low carbohydrate intake on plasma glucose and amino acid, and urinary organic acid levels, including dicarboxylic and tricarboxylic acid cycle intermediates, was determined in eight normal adult volunteer subjects. Urine was collected at baseline and at 48 to 72 hours for amino acid and organic acid levels, and plasma collected at 0 and 72 hours for glucose and amino acid concentration. The MCT diet increased urinary levels of dicarboxylic acids (adipic 8-, suberic 65-, sebacic 284-fold) and keto acids (acetoacetate and beta-hydroxybutyrate, 67.5-fold); alanine and lactate were decreased 2.5- and 4-fold, respectively, while pyruvate, other amino acids and citric acid intermediates remained unchanged. Plasma amino acid levels were unchanged, while the plasma glucose levels decreased by 8% from baseline. The loss of calories as urinary dicarboxylic acids and keto acids, although increased during the MCT diet, was less than 1% of the daily caloric intake. The data suggest MCT sustain energy expenditure through medium-chain fatty acid (MCFA) oxidation with no decrease in citric acid cycle intermediates, while sparing protein oxidation.

Plasma L-arginine concentration, oxygenation index, and systemic blood pressure in premature infants

OBJECTIVE To determine the relationships between plasma L-arginine concentrations and the severity of respiratory distress syndrome (RDS) or systemic blood pressure in premature infants. DESIGN Prospective, observational study. SETTING Neonatal intensive care, tertiary referral hospital. SUBJECTS Fifty-three premature infants. INTERVENTIONS We measured arginine and nutritional intake, plasma arginine concentration, total amino acid concentrations, and blood pressure on days 3, 7, 14, and 21 of life. In 33 infants who received assisted ventilation, oxygenation index could be calculated to reflect the severity of RDS. The relationships between plasma arginine and oxygenation index or blood pressure were analyzed using multiple linear regression. MEASUREMENTS AND MAIN RESULTS On day 3, plasma arginine concentrations were decreased compared with normal published values. Arginine concentrations increased with the day of life of measurement (p < .001) and with arginine intake (p < .001). After adjusting for arginine intake and day of life, an inverse relationship was found between oxygenation index and plasma arginine concentrations: (p = .025). No similar relationship was found between oxygenation index and the concentration of total amino acids. A weak positive relationship was found between plasma arginine concentration and systemic blood pressure. CONCLUSIONS Increments in the oxygenation index, reflective of an increased severity of RDS, are associated with a decrease in plasma arginine concentration. This finding may reflect arginine consumption by the nitric oxide synthase pathway in the lungs of premature infants with RDS, or may be explained by increased arginine catabolism. The lack of a similar relationship between total plasma amino acids and oxygenation index supports the first interpretation.

Catch-up Growth in Children Treated With Home Enteral Nutrition

Objective. This study was designed to determine the effect of home enteral nutrition on the outcomes of growth and the relationship between growth and entrance anthropometric criteria. Methods. We reviewed the medical records of 78 consecutive children (median age, 20 months) who were enrolled in the home enteral feeding program at the Alberta Childrens Hospital (Calgary, Alberta, Canada) between 1993 and 1995. Weights, heights, and weight-for-heights were expressed as Z scores, using the Centers for Disease Control and Prevention anthropometric growth curve software. To evaluate growth outcome, the total group was further subdivided using anthropometric criteria into appropriate, wasted, or stunted at the time of entry to the program. In a subgroup of 36 children on whom anthropometric data was available for a median length of 5.7 months,Z scores were compared at 3 points in time: before entry, at time of entry, and last follow-up. Results. Patients were classified into five main groups: 11 (14%) had pulmonary disease, 26 (33%) had a gastrointestinal disorder, 21 (27%) had congenital defects, 10 (13%) had a neurologic disorder, and the remaining 10 (13%) had a variety of other illnesses, including malignancies and metabolic disorders. Patients were on the program for a median duration of 8.9 months. It was found that during the period of support within the program, enteral feeding was successful in improving weight-for-age Z scores by 0.42 standard deviations but the effect on height-for-age Zscores and weight-for-height Z scores did not reach significance for this population. The subgroup of 36 children on whom longitudinal anthropometric data was available before entering the program was found to have had a significant drop in weightZ scores between the time before program entry (median length of time, 5.7 months) and the time of program entry, which indicates that these children were falling off the growth curve before commencing enteral feeding. To evaluate growth outcome, the total group was further subdivided using anthropometric criteria into appropriate, wasted, or stunted at the time of entry to the program. In the group of appropriate growth patients, while in the program, 50% had catch-up growth for weight (positive change in Z scores) and 33% for height. In the wasted patients, 92% improved their weight percentile and 75% their height percentile. In the stunted group, 71% had catch-up growth for weight and 74% for height. Conclusion. We concluded that the enteral feeding program was able to promote catch-up growth or maintain growth along percentiles in the majority of children.

Tolbutamide causes a modest increase in insulin secretion in cystic fibrosis patients with impaired glucose tolerance.

We examined the effect of intravenous (i.v.) tolbutamide administration on glucose and hormone levels in cystic fibrosis (CF) patients with impaired first-phase insulin secretion and oral glucose tolerance (oral glucose tolerance test [OGTT]) and compared them with CF patients with only an impaired first-phase insulin secretion and healthy control subjects. Five CF patients with an impaired OGTT, ie, a serum glucose value of 7.8 mmol/L or greater 120 minutes after an oral glucose load (group I), five CF patients with a normal OGTT, ie, a serum glucose not exceeding 7.8 mmol/L 120 minutes after oral glucose (group II), and five healthy control (CON) subjects underwent IV glucose tolerance tests with glucose alone (IVGTT) and glucose administered in conjunction with tolbutamide ([IVTTT] 25 mg/kg; maximum dose, 1 g). Serum glucose levels were measured using the glucose oxidase method; insulin, C-peptide, and glucagon levels were measured by the double-antibody radioimmunoassay (RIA) technique. Serum immunoreactive trypsin (IRT) and hemoglobin A1 (HbA1) levels and height and weight were measured for each subject, and in addition, pulmonary function was assessed in those with CF. There were no significant differences in the area under the curve (AUC) for glucose or glucose or glucagon levels or the serum glucose disappearance rate (k value) between group I, group II, or CON subjects during the IVGTT. First-phase insulin and C-peptide secretion was abnormal during IVGTT and IVTTT in the CF groups: in group I it was severely impaired, whereas in group II it was between group I and CON values. During the IVTTT serum glucose levels and glucose k values were not significantly altered in any of the three groups as compared with the IVGTT.(ABSTRACT TRUNCATED AT 250 WORDS)

Early onset of essential fatty acid deficiency in patents with cystic fibrosis receiving a semisynthetic diet

disordered functioning of individuals with PKU has been debated 9, ~0 and should continue to be investigated. Without a matched control group, it is difficult to determine whether the women were affected by PKU or hyperphenylalaninemia in relatively subtle ways. It is possible that they would have been more intelligent, better educated, more financially stable, and emotionally more secure if they were biochemically normal. Nevertheless, these results are potentially useful because they might provide a basis for comparison with adults who have nonclassic PKU and who received dietary treatment after newborn screening identification. It is unlikely that there will be another opportunity to study a cohort of adults with untreated atypical PKU. As a group the women adequately performed lifes tasks and were making suitable adjustments in their roles as mothers, wives, and members of their communities.

Mitochondrial abnormalities of liver in two children with citrullinaemia.

Citrullinaemia is a rare inborn error of urea-cycle metabolism. Two affected children are reported in whom progressive metabolic instability suggested the possibility of hepatopathy or an ongoing hepatic mitochondrial injury. A percutaneous liver biopsy was performed in each patient. Electron-microscopic findings were similar in both cases. Approximately 20% of the mitochondria were abnormally enlarged with paracrystalline inclusions and electron-dense bodies of different sizes and shapes present in the matrix. The specificity of these findings is discussed in the context of previous reports of ultrastructural abnormalities in the hepatocytes of patients with inborn errors of the urea cycle. It is speculated that the mitochondrial abnormalities in citrullinaemia may be related to the accumulation of citrulline in the mitochondria which may eventually manifest as metabolic instability.