Urinary 3-methylhistidine excretion in juvenile-onset diabetics: evidence of increased protein catabolism in the absence of ketoacidosis

Stepwise Discovery of Insulin Effects on Amino Acid and Protein Metabolism

A clear effect of insulin deficiency and replacement on body/muscle mass was a landmark observation at the start of the insulin age. Since then, an enormous body of investigations has been produced on the pathophysiology of diabetes mellitus from a hormonal/metabolic point of view. Among them, the study of the effects of insulin on body growth and protein accretion occupies a central place and shows a stepwise, continuous, logical, and creative development. Using a metaphor, insulin may be viewed as a director orchestrating the music (i.e., the metabolic effects) played by the amino acids and proteins. As a hormone, insulin obviously does not provide either energy or substrates by itself. Rather, it tells cells how to produce and utilize them. Although the amino acids can be released and taken up by cells independently of insulin, the latter can powerfully modulate these movements. Insulin regulates (inhibits) protein degradation and, in some instances, stimulates protein synthesis. This review aims to provide a synthetic and historical view of the key steps taken from the discovery of insulin as an "anabolic hormone", to the in-depth analysis of its effects on amino acid metabolism and protein accretions, as well as of its interaction with nutrients.

Cystic fibrosis related diabetes

Diabetes is a frequent complication seen in cystic fibrosis patients as they reach adulthood. Cystic fibrosis related diabetes (CFRD) is distinguished as a separate entity with features that include progressive loss of islet beta cell mass and insulin deficiency, as well as insulin resistance. Abnormalities in glucose tolerance may be detectable for many years prior to the development of overt diabetes. Therefore oral glucose tolerance testing is the preferred screening method for the identification of those patients at the highest risk for progression to diabetes. Progression to diabetes has been linked to poor outcomes in CF including loss of pulmonary function and increased mortality among females. Given the role that insulin deficiency plays in CFRD, insulin replacement therapy remains the only recommended intervention. In the absence of definitive supportive data, the use of oral antidiabetic agents is not considered standard therapy and needs further study. As with other forms of diabetes, CFRD patients also experience microvascular complications and should be periodically evaluated for manifestations.

Diabetic ketoacidosis depletes plasma tryptophan

Diabetic ketoacidosis (DKA) is a severe metabolic disturbance of insulin-dependent diabetes mellitus (IDDM) which has a significant effect on amino acid metabolism. Amino acids serve as precursors for various neurotransmitters which are involved in affective disorders, and patients with IDDM are known to have an increased prevalence of affective disorders. We monitored the plasma concentrations of 23 amino acids in six adolescents prior to treatment of DKA and at 6, 24 and 120 hours after initiation of treatment. The well-known increase in the concentrations of the glucogenic amino acids and the decrease in the branched-chain amino acids were observed in response to treatment of DKA. Low levels of tryptophan were found prior to treatment of DKA. Treatment increased the plasma tryptophan levels, but the mean concentration remained low throughout the sampling period. Only the glutamate-derived amino acids (glutamate, proline and glutamine) from the Krebs cycle pool were significantly affected by treatment. Glutamine declined initially, but recovered as the plasma pH normalized. Our results indicate that DKA causes a depletion of plasma tryptophan. This depletion may predispose some patients with IDDM to have affective disorders secondary to a neurotransmitter imbalance.

Body composition and fat distribution measured by dual-energy x-ray absorptiometry in premenopausal and postmenopausal insulin-dependent and non-insulin-dependent diabetes mellitus patients

The study aim was to measure body composition and fat distribution in premenopausal and postmenopausal women with insulin-dependent ([IDDM] n = 53) and non-insulin-dependent ([NIDDM] n = 32) diabetes mellitus by dual-energy x-ray absorptiometry. IDDM and NIDDM patients had similar, normal lean tissue mass (LTM) and 24-hour urinary excretion of creatinine. Total body and abdominal fat percentages were higher in the NIDDM group (approximately 40%) than in the IDDM group (-27%, P < .001) and were constant with age and menopausal status in both groups. In postmenopausal patients with IDDM, total body and abdominal fat values were less than in postmenopausal healthy women (approximately 27% v approximately 37%, P < .001). In premenopausal patients with NIDDM, total body and abdominal fat were higher than in premenopausal healthy women (approximately 42% v approximately 25%, P < .001). In conclusion, women with IDDM or NIDDM have a normal LTM and probably a normal muscle mass. Total body and abdominal fat were higher for women with NIDDM than for those with IDDM.

Creatinine height index and lean body mass in adult patients with insulin-dependent diabetes mellitus followed for 7 years from onset

The 24-hour urinary creatinine excretion value can be used as an index of protein nutrition; the creatinine height index and lean body mass can be estimated from this value. On the basis of longitudinally measured 24-hour urinary creatinine excretions during the initial 7 years of type 1 diabetes in an incidence cohort of 147 adult patients, we studied creatinine height index and lean body mass and possible relationships to sequential measurements of glycated hemoglobin (HbA1c). The patients were divided into four groups according to their glycemic control during these 7 years: I, HbA1c < 7.4% (n = 37); II, HbA1c 7.4% to 8.2% (n = 37); III, HbA1c 8.3% to 8.9% (n = 38); IV, HbA1c > 8.9% (n = 35). One year after the onset of diabetes, height indices were as follows (% of normal values, median and quartiles): I, 104% (90 to 116); II, 101% (78 to 105); III, 121% (92 to 128); IV, 87% (78 to 109) ([IV] < [I to III]; p < .05). During the following 6 years no significant differences in height index were observed among the four groups of patients at any point in time. Slightly higher calculated lean body mass values were found in the most well-controlled patients, but otherwise no differences were found in lean body mass. It is concluded that, apart from the first year, indices of protein nutrition remain normal during the initial 7 years of type 1 diabetes, even in patients with poor glycemic control.

Energy expenditure in children with type I diabetes: evidence for increased thermogenesis

The aim of the study was to assess whether increased energy expenditure causes the negative energy balance (tissue catabolism) commonly seen in children with insulin dependent (type I) diabetes. Resting metabolic rate and thermogenesis induced by adrenaline were measured in five healthy children and 14 children with type I diabetes who were all free of clinical signs of late complications of diabetes mellitus but differed in their degree of glycaemic control (in eight glycated haemoglobin concentration was less than 10% and in the six others greater than or equal to 10%). When compared with the control subjects children with type I diabetes had normal resting metabolic rates but their urinary nitrogen excretion was significantly raised (11.5 (SD 5.4) mg/min in those with glycated haemoglobin concentration less than 10%, 11.6 (5.2) mg/min in those with concentration greater than or equal to 10% v 5.4 (3.0) mg/min in control subjects). During the infusion of adrenaline the diabetic children showed a threefold and sustained increase in thermogenesis and disproportionate increases in the work done by the heart, in lipid oxidation rate, and in plasma concentrations of glucose, free fatty acids, and ketone bodies. The increased thermogenic effect of adrenaline did not correlate with the degree of glycaemic control. Increased thermogenesis may explain the tissue wasting commonly seen in children with type I diabetes during intercurrent stress.

Protein turnover in acid maltase deficiency before and after treatment with a high protein diet

A patient with acid maltase deficiency was treated with a high protein diet for 7 months. Protein turnover expressed in terms of lean body mass was shown to be increased in this patient before the diet but was markedly reduced following the diet. The patient improved clinically whilst on the diet both subjectively and in terms of mobility, breathing and reduced peripheral cyanosis at rest.

Rat muscle protein turnover and redox state in progressive diabetes

Protein synthesis and degradation, and redox state were measured in soleus and extensor digitorum longus muscles of rats up to 12 days after injection of streptozotocin. Muscle growth was slower in these animals apparently due to slower protein synthesis throughout the duration of diabetes. Up to day 4 after injection of streptozotocin or withdrawal of insulin from treated, diabetic animals, the muscle ratio of lactate/pyruvate, an indicator of the cytoplasmic NAD+ redox couple, was lower and protein degradation was faster than in control muscles. Thereafter, the ratio of lactate/pyruvate was greater and protein degradation was slower than in size- or age-matched control muscles. Insulin treatment in vitro or in vivo increased lactate/pyruvate and decreased proteolysis. Therefore, in muscles of streptozotocin-diabetic rats, the initial increase and later fall in proteolysis, and the inhibition of proteolysis by insulin, may correlate with opposite changes in NADH/NAD+.

The metabolic status of internal intensive care patients as indicated by 3-methylhistidine excretion and nitrogen balance

The metabolic status of 15 intensive care patients receiving a standardized total parenteral nutrition regimen was followed up to 15 days immediately after admission by measuring 3-methylhistidine, total nitrogen, and creatinine excretion. The average 3-methylhistidine excretion was within the normal range during the first 3 days, rising on day 4 and reached a maximum of 70% above normal values on day 5. It declined to within normal range thereafter in most of the patients. Mean values for creatinine excretion remained relatively constant within the normal range throughout the study. During all days 3-methylhistidine was negatively correlated with N-balance. It is concluded that these patients had increasing catabolism with a maximum on day 5 and that the catabolic condition was associated with an increased muscle protein breakdown.

Sulfur amino acid metabolism in juvenile-onset nonketotic and ketotic diabetic patients

Sulfur amino acid metabolism was studied in non-fasting nonketotic and ketotic juvenile-onset diabetic children and the results were compared to age-matched healthy children on an ordinary diet. An increased excretion of total sulfur and inorganic sulfate was found in diabetic children, probably a result of a decreased protein-serum synthesis and/or increased endogenous protein catabolism, although as a result of hyperglycemia a decreased tubular reabsorption may also have contributed. All diabetics showed a normal excretion of methionine. For cyst(e)ine and taurine an increased excretion was seen in ketotic diabetics, probably also a consequence of an increased endogenous protein degradation. As a sign of the latter, an increased output of 3-methylhistidine was also observed, a confirmation of earlier reports. The increased output of mercaptolactate and mercaptoacetate found in ketotic patients, was probably also a result of enhanced endogenous protein degradation. An increased urinary excretion of N-acetylcysteine was seen in diabetic children, which may reflect an enhanced availability to acetyl coenzyme A.

Urinary 3-methylhistidine excretion in man: the role of protein-bound and soluble 3-methylhistidine

The influence of dietary meat and meat stock intake on urinary excretion of 3-methylhistidine (3MH) was examined in human adults. In the absence of 3MH ingestion for 48 h, the study subjects adjusted to an intrinsic urinary 3MH: creatinine value. If the meat and meat stock-free diet was maintained on subsequent days, only minute diurnal variations occurred, and the values of random urine samples during the day were representative of the 24 h 3MH: creatinine value. The mean 3MH: creatinine value (SD) for a group of adults (n 7) was 0.105 +/- 0.023 (mumol of 3MH/mg creatinine), which is approximately 35% lower than the corresponding value in healthy growing infants (0.148 +/- 0.039) (Seashore et al. 1981). Ingestion of meat soup and meat causes different patterns of urinary excretion of 3MH which are consistent with the finding that meat extracts, such as soup and stock, contain considerable amounts of 3MH. The 3MH contents of beef, chicken and turkey were 3.8 +/- 0.15, 3.0 +/- 0.09 and 2.3 +/- 0.29 mumol/g dry wt meat respectively. All three meats contained a water-soluble 3MH-fraction (% total 3MH: beef 8, chicken 21, turkey 23). Amino acid analysis of the soluble fraction with or without hydrochloric acid hydrolysis demonstrated free 3MH in chicken and turkey (5.2 and 2.8% of the total respectively) but not in beef. Patients undergoing urinary 3MH measurements should maintain a diet that is free not only of solid meats, but also of meat stock. The ingestion of commercial food products (e.g. frozen or canned meals, sauces, pizza, etc.) may impair the validity of such measurements because of their meat-stock content. A dietary regimen is presented which is based on a shorter 12 h urine collection. The shorter collection time is satisfactory in the light of the steady rate of 3MH-excretion after 2 d of a diet free of meat and meat stock.