Branched-chain-ketoacid metabolism in patients with chronic renal failure

Branched-chain ketoacids (BCKAs) were determined in fasting plasma samples from 19 patients with chronic renal failure (CRF). Ketomethylvalerate (KMV) was significantly higher in patients receiving BCKA supplements, presumably reflecting accumulation of the R(-) isomer. Mean levels of all three BCKAs were not significantly different from normal. However, multiple-regression analysis showed that plasma ketoisocaproate was strongly correlated with glomerular filtration rate (GFR), negatively correlated with serum triglyceride concentration, and positively correlated with protein intake. KMV concentration was also correlated positively with GFR, negatively with triglyceridemia, and positively with serum total carbon dioxide. Ketoisovalerate concentration did not vary with GFR and was not predictable from the regressors used. Single oral doses of a mixture containing all three BCKAs led to the same areas under the three plasma concentration curves in patients with CRF as in normal subjects, indicating that absorption of all three BCKAs after oral administration in patients with CRF is unimpaired.

Utilization for protein synthesis in individual rat organs of extracellular 2-ketoisocaproate relative to utilization of extracellular leucine

Rats were given constant intravenous infusions of [3H]-leucine plus [1-14C]-2-ketoisocaproate (KIC). Specific activities of plasma leucine and plasma KIC reached plateaus by two to three hours. 3H specific activity of KIC was 85% +/- 2% of that in leucine. 14C specific activity of leucine was 36% +/- 2% of that in KIC. The 14C/3H ratios in leucine and KIC were constant from the earliest sampling time (one hour) at 0.65 +/- 0.03 and 2.20 +/- 0.07, respectively. In various tissues, 14C/3H in free leucine and in tissue protein were approximately equal, but in most organs these ratios were significantly greater than the ratio 14C/3H in plasma leucine. From these data we estimate that the fraction of leucine incorporated into protein in individual organs derived from extracellular KIC rather than extracellular leucine varies from zero (in liver and bone marrow) to 35% to 45% (in brain and heart), and comprises 12% in the body as a whole.

Progression of chronic renal failure is related to glucocorticoid production

Progression of chronic renal failure during 35 treatment periods in 27 patients was measured as the rate of change of bimonthly radioisotope GFR for an average of 15 months. Treatments were comprised of: (1) mild protein restriction; (2) more severe protein and phosphorus restriction plus essential amino acids; or (3) the same diet plus ketoacids. Progression was significantly (P less than 0.025) correlated with urinary 17-hydroxycorticosteroid excretion in all three treatment groups; overall r was 0.78 (P less than 0.0001). Multiple regression analysis showed that the following factors were not additional significant determinants of progression: urea N excretion, phosphate excretion, protein excretion, serum calcium times phosphorus product, serum alkaline phosphatase, serum uric acid, serum triglycerides, serum cholesterol, etiology, mean arterial pressure, or enalapril treatment. However, when urinary 17-hydroxycorticosteroid excretion was factored by GFR (with which it was correlated), additional significant regressors appeared: serum triglycerides and polycystic kidney disease, which tended to be associated with more rapid progression, and ketoacid treatment, which tended to be associated with slower progression. Mean 17-hydroxycorticosteroid excretion differed significantly between the three treatment groups, in the order (1) greater than (2) greater than (3) (though not when factored by GFR). Changing from essential amino acids to ketoacids (or vice versa) without change in diet was associated with lower 17-hydroxycorticosteroid excretion on ketoacids (but not when factored by GFR).(ABSTRACT TRUNCATED AT 250 WORDS)

Radioisotopic measurement of glomerular filtration rate in severe chronic renal failure

In order to determine the best method for routine measurement of glomerular filtration rate (GFR) in severe renal failure, we compared simultaneously the urinary clearances of [99mTc] diethylenetriaminepentaacetic acid (DTPA) (UD), [125I]iothalamate (UI), 24-hr creatinine clearance (UC) and plasma clearance of [99mTc]DTPA (PD), based on three plasma samples. In 60 studies in 22 patients with serum creatinine values of 2 to 8 mg/dl, UD and UI were almost identical: UD = 0.358 +/- 0.976 UI +/- 0.87 ml/min, r = 0.990. However, PD overestimated UD by a large and variable extent: PD = 11.3 +/- 0.843 UD +/- 5.5 ml/min, r = 0.694, and was inconsistent in sequential measurements in individual patients. UC also overestimated urinary isotope clearance: UC = 4.2 + 0.95 UI +/- 3.9 ml/min, r = 0.865. Sequential measurements of GFR in five patients with severe but stable renal failure (mean GFR 5.9 ml/min) showed an average standard deviation of only 0.83 ml/min. Thus both UD and UI appear to be reliable and precise measures of GFR in severe renal failure.

Utilization for protein synthesis of 2-ketoisocaproate relative to utilization of leucine, as estimated from exhalation of labelled CO2

1. We have previously shown that the ratio (RWBP) of incorporation of label from 2-ketoisocaproate (KIC) into the leucine of whole-body protein to the simultaneous incorporation of label from leucine itself into protein is a measure of the nutritional efficiency of KIC as a substitute for leucine. 2. In order to determine whether RWBP can be estimated indirectly from measurement of labelled CO2 excretion, rats were injected orally or intravenously with [4,5-3H]leucine and either [1-14C]leucine or [1-14C]KIC. Expired CO2 was collected for 6 h. 3. The results show that 9-14% of KIC underwent first-pass oxidation after oral administration. When isotopes were given intravenously, the mean rate of excretion of 14CO2 from KIC, after 20 min, remained 1.8 times the mean rate of excretion of 14CO2 from leucine. 4. Mean RWBP, measured in whole-body protein in rats given isotopes orally or intravenously along with small or large doses of carriers, was the same as mean RWBP estimated from mean cumulative CO2 excretion. 5. We conclude (1) that nutritional efficiency of KIC relative to leucine can be estimated from measurement of labelled CO2 excretion, and (2) that the relative inefficiency of KIC as a substitute for leucine in the rat is attributable to first-pass oxidation of 9-14% (when given orally) and 80% greater susceptibility to systemic oxidation than leucine.

Creatinine measurements often yielded false estimates of progression in chronic renal failure

In 9 of 22 observation periods (lasting an average of 15 months) in 17 patients with moderate to severe chronic renal failure (GFR 4 to 23 ml/min), rates of progression as estimated from the linear regression on time of 24-hour creatinine clearance (b1) differed significantly from rates of progression as estimated from the regression on time of urinary clearance of 99mTc-DTPA (b2), during all or part of the period of observation. b1 exceeded b2 in four cases and was less than b2 in the other five. Thus there were gradual changes in the fractional tubular secretion of creatinine in individual patients, in both directions. Owing to these changes, measurements of creatinine clearance gave erroneous impressions of the rate or existence of progression during all or a portion of the period of observation in nearly half of these patients. In the 22 studies as a group, using the entire periods of observation, b1 indicated significantly more rapid progression (by 0.18 +/- 0.06 ml/min/month, P less than 0.01) than did b2, and had a significantly greater variance. Measurements of progression based on the rate of change of reciprocal plasma creatinine (multiplied by an average rate of urinary creatinine excretion in each study) were equally misleading, even though less variable. We conclude that sequential creatinine measurements are often misleading as measures of progression and should, when feasible, be replaced by urinary clearance of isotopes in following patients with chronic renal failure.

Rate of whole-body protein synthesis in the rat as calculated from fractional oxidation of leucine, valine, or methionine

In the steady state, the ratio of the rate of utilization for whole-body protein synthesis of any essential amino acid to its rate of oxidation should be the same as the ratio of the peak fraction of a dose of tracer incorporated into protein (F) to the fraction oxidized (1-F) provided that negligible tracer remains in the free amino acid pool or remains unabsorbed in the gut. The total rate of amino acid catabolism (C) can be estimated from the rate of urinary excretion of urea nitrogen (N) plus ammonia N. Hence the rate of whole-body protein synthesis (S) can be estimated as CF/(1-F). This method, which is not new, was explored as follows: (1) Radioactivity in the leucine of whole-body protein of rats after intravenous (IV) injection of labeled leucine was shown to plateau from three to nine hours. (2) The fractions of labeled leucine, valine, and methionine remaining in the gut six hours after enteral injection were 1.2 +/- 0.4% (SD), 1.2 +/- 0.4%, and 7.1 +/- 2.9%, respectively; thus, enterally administered methionine cannot be used for this purpose. (3) Oxidation of [1-14C]-labeled leucine or valine, measured from 14CO2 excretion, was found to be the same whether these isotopes were given IV or enterally. (4) Negligible radioactivity remained in the free leucine of plasma within one hour after injection of labeled leucine.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of ketoleucine treatment on atrophy of skeletal muscle

There is a net loss of skeletal muscle protein in muscle-wasting disorders including the muscular dystrophies and denervation atrophy. Regardless of the nature of the underlying defect, a treatment that could reduce the rate of muscle protein degradation may be of therapeutic value in these conditions. Ketoleucine (alpha-ketoisocaproic acid) has been reported to reduce the rate of protein degradation in skeletal muscle. To evaluate ketoleucine's therapeutic potential, we studied its effect on the muscle protein loss that follows denervation in rats. Maximum tolerated doses of ketoleucine were administered twice daily to rats after surgical denervation of one leg. Wet weights and noncollagen proteins of the soleus and extensor digitorum longus muscles were measured. The ketoleucine-treated animals failed to show significant decrease in muscle wasting, compared with nontreated denervated controls. Further, urinary 3-methylhistidine excretion, a putative measure of muscle breakdown, was not reduced in ketoleucine-treated animals. Our findings do not support the suggested therapeutic role for ketoleucine in muscle-wasting disease.

Progression of chronic renal failure in patients given keto acids following amino acids

Twelve patients with chronic renal failure who exhibited a progressive decline in 24-h creatinine clearance despite being given, for 2-10 months, a diet containing 0.3 g of protein/kg ideal weight and 7-9 mg of phosphorus/kg ideal weight supplemented with vitamins, CaCO3, and 10 g per day of essential amino acids, were changed to a supplement containing predominantly keto acids. In 6 patients whose serum creatinine levels were 7.5 mg/dl or greater at changeover, progression continued unabated. In 6 patients with serum creatinine levels at changeover of 6.5-7.4 mg/dl, one was non-compliant with the diet and progressed to dialysis. In the other 5, progression, measured as the rate of change of a bimonthly radioisotope clearance, has been undetectable during the ensuing 1-2 years.

Creatinine excretion as a measure of protein nutrition in adults of varying age

The use of the creatinine height index (CHI) as a measure of protein nutrition is reviewed. Any such cross-sectional measurement is inherently limited. Using published values for urinary creatinine excretion per kilogram body weight in adult subjects of varying age and values for "ideal" weight as a function of height, we have derived normal values for expected creatinine excretion in men and women of varying height. These permit the derivation of an age-corrected CHI. Possible explanations for the normal decrease in creatinine excretion with age include (1) decreasing lean body mass with age, (2) decreasing proportion of muscle in lean body, and (3) lower meat intake in older persons. Diet has an important influence if meat intake is substantial or if consumption of a creatine-free diet is prolonged. Creatinine metabolism and extrarenal excretion are minor, except in subjects with reduced renal function. Application of a correction for constant extrarenal clearance of creatinine in patients with chronic renal failure probably is not valid. Further observations of creatinine excretion in normal subjects of varying age and height are needed.

Measurement of branched-chain ketoacids in plasma by high-performance liquid chromatography

Branched-chain ketoacids were isolated from plasma or serum samples by acidification, passage through a cationic exchange resin, ether extraction, and extraction of the ether layer with phosphate buffer. The recovery of 2-[1-14C]ketoisocaproate taken through these procedures averaged 95 +/- 3%. Branched-chain ketoacids were measured by high-performance liquid chromatography using a single mobile phase (sodium phosphate:acetonitrile). In normal human subjects, mean +/- SD fasting levels of 2-ketoisocaproate, 2-keto-3-methylvalerate, and 2-ketoisovalerate were 29 +/- 8, 18 +/- 4, and 12 +/- 3 microM, respectively. In normal rats, slightly different results were found: 24 +/- 10, 19 +/- 7 and 17 +/- 6 microM, respectively. In both species, levels of each ketoacid expressed as fractions of total branched-chain ketoacids were much less variable.

Progression of chronic renal failure in patients given ketoacids following amino acids

Twelve patients with chronic renal failure who exhibited a progressive decline in 24-hour creatinine clearance, despite being given for 2 to 10 months a diet containing 0.3 g per kg ideal weight of protein and 7 to 9 g mg per kg ideal weight of phosphorus, supplemented with vitamins, CaCO3, and 10 g per day of essential amino acids, were changed to a supplement containing predominantly ketoacids. In six patients whose serum creatinine was 7.5 mg/dl or greater at changeover, progression continued unabated. In six patients with serum creatinine levels at changeover of 6.6 to 7.4 mg/dl, one was non-compliant with the diet and progressed to dialysis. In the other five, progression, measured as the rate of change of a bimonthly radioisotope clearance, has been undetectable during the ensuing one to two years. There has been no change in urea appearance, blood pressure, phosphaturia or proteinuria. Nutrition has been maintained. Thus this ketoacid supplemented regimen apparently halted the progression of moderately-severe chronic renal failure for at least a year in a small group of patients in whom restriction of protein and phosphate intake without ketoacids failed to halt progression. In more severe renal failure, no effect on progression was seen.

Utilization of alpha-ketoisocaproate for protein synthesis in uremic rats

We have recently shown that the nutritional efficiency, R, of alpha-ketoisocaproate (KIC) as a substitute for leucine, defined as the ratio of the dose of leucine to the dose of KIC (on a leucine-free diet) for equal growth, can be evaluated isotopically: 14C-KIC and 3H-leucine are administered p.o.; six hours later, 14C/3H in the leucine of whole body protein, divided by 14C/3H in the injectate, gives a value distinguishable from R assessed in the same animals by growth experiments. To see how chronic uremia affects R, 11/12 nephrectomized rats and sham-operated controls were fed a regular diet for 15 days and then given these isotopes p.o. Six hours later, R, measured in whole body protein, and in the protein of brain, heart, muscle, salivary gland, liver, and the kidney remnant was significantly greater than in sham-operated controls. The greatest difference (39%) was seen in liver protein and the smallest difference (19%) in muscle. Thus chronic uremia increases the efficiency, relative to leucine, with which KIC is utilized for protein synthesis in all of these organs and in the body as a whole. Possible explanations are discussed.

Utilization of alpha-ketoisocaproate for synthesis of hepatic export proteins and peripheral proteins in normal and cirrhotic subjects

The ratio R, defined as (percent of dose of 14C)/(percent of dose of 3H) in the leucine of plasma fibrinogen, albumin, immunoglobulin G (IgG), red cell globin, and salivary mucin, was measured in 7 normal adults and in 5 cirrhotic patients during continuous intragastric infusion of 1-14C-labeled alpha-ketoisocaproate (KIC) and 3H-labeled leucine. The ratio R measured in whole body protein has been shown in rat experiments to be a measure of the nutritional efficiency of KIC relative to leucine. In normal subjects, R in albumin and fibrinogen became constant (0.63 +/- 0.05) after the third hour and were indistinguishable from one another. The ratio R in IgG was similar and constant. The ratio R in plasma leucine (0.62 +/- 0.06) was significantly lower than R in mucin (0.86 +/- 0.04) or globin (0.73 +/- 0.04), indicating that these latter proteins derive a significant fraction of their leucine from KIC transaminated locally, rather than from circulating leucine. Results in 5 cirrhotic patients were the same, except that R in IgG and R in globin were significantly increased. Thus, cirrhosis does not alter the efficiency, relative to leucine, with which oral KIC is used for synthesis of export proteins by the liver, but increases the efficiency with which it is used for the synthesis of some proteins peripherally.

Effect of experimental liver disease on the utilization for protein synthesis of orally administered alpha-ketoisocaproate

The incorporation of orally administered 1-14C-alpha-ketoisocaproate into the leucine of proteins in rats was compared with the incorporation of [3H]leucine itself administered simultaneously and expressed as a ratio, R. This ratio in whole body protein has been shown to be approximately equal to the nutritional efficiency of alpha-ketoisocaproate as a dietary substitute for leucine. In normal rats on a 14% protein diet, R in whole body protein (0.30 +/- 0.01) and in the protein of various organs was the same whether the isotopes were given by single injection or 6-hr constant infusion. Thus, both techniques yield the same time-independent parameter, R, which measures the relative efficiency of alpha-ketoisocaproate as a substitute for leucine. R varied between organs as follows: liver (0.22 +/- 0.01) less than kidney less than heart less than salivary gland less than brain less than muscle (0.42 +/- 0.01). In rats with galactosamine-induced acute liver failure (Group I), carbon tetrachloride-induced cirrhosis (Group II), or portal-systemic shunts (Group III), whole body protein R and R in the protein of organs other than the liver was generally increased compared with controls, as was R in circulating IgG in Group III; R in liver protein was unchanged (Groups II and III) or slightly lower than controls (Group I). Thus, severe liver disease and portal-systemic shunting both increase the utilization of alpha-ketoisocaproate for synthesis of protein in the body as a whole and in most organs. In the liver, however, alpha-ketoisocaproate utilization for protein synthesis is unaffected or slightly reduced.

Effect of the level of dietary protein on the utilization of alpha-ketoisocaproate for protein synthesis

The efficiency of alpha-ketoisocaproate (KIC) as a dietary substitute for leucine in rats on varying protein intake was estimated by an isotopic method, previously shown to yield the same results as comparative growth experiments. 14C-KIC and 3H-leucine are injected orally. Six hours later the ratio, R, of 14C/3H in isolated proteins, divided by the same ratio in the injectate is measured. This ratio has been shown to be approximately equal to nutritional efficiency of KIC relative to leucine. As dietary protein increased from 6.3% to 48.3%, whole body protein R decreased from 0.515 +/- 0.045 to 0.299 +/- 0.016. Variations with protein intake were noted in R of protein isolated from individual organs. The magnitude of R in these organs varied two-fold, in the following sequence: brain greater than heart greater than or equal to skeletal muscle greater than or equal to salivary gland greater than or equal to kidney greater than liver. Whole body protein R could be confidently predicted (r2 = 0.992) from R in the protein of kidney and muscle. Thus the nutritional efficiency of KIC as a dietary substitute for leucine in individual organs as well as in the whole animal is strongly dependent on the level of protein intake.

Nutritional efficiency of alpha-ketoisocaproate relative to leucine, assessed isotopically

The efficiency of alpha-ketoisocaproate as a dietary substitute for leucine was assessed in rats by two techniques: first, the minimal dose of alpha-ketoisocaproate required, as a supplement to a leucine-free diet, to achieve a growth rate as great as animals receiving leucine was found to be between 2.2 and 4.4 times larger. Therefore the nutritional efficiency of alpha-ketoisocaproate lies between 0.23 and 0.46. Second, alpha-[1-14C]-ketoisocaproate and [3H]leucine were administered orally and the ratio of 14C/3H incorporated into the leucine of whole-body protein and fibrin was measured. This ratio, divided by the ratio 14C/3H injected, was the same in fibrin as in whole-body protein and averaged 0.39. Thus both techniques yield the same value, within the error of measurement, for the relative nutritional efficiency of alpha-ketoisocaproate. We also found that alpha-ketoisocaproate feeding at varying dosage did not alter this ratio in whole-body protein (measured in rats fasted overnight), suggesting that neither wide variations in growth rate nor exposure for 10 days to alpha-ketoisocaproate (in a diet of constant protein content) alters the relative rates of utilization (or oxidation) of alpha-ketoisocaproate vs. leucine.

The effect of a keto acid-amino acid supplement to a restricted diet on the progression of chronic renal failure

We treated 24 patients who had chronic renal failure with a low-phosphorus diet containing 20 to 30 g of mixed-quality protein, supplemented by amino acids and their keto analogues. Seventeen patients had well-defined rates of progression before treatment, as assessed by serial determinations of serum creatinine levels. By extrapolating these rates of progression, we found that 10 of the 17 (59 per cent) had a clinically important slower rise in creatinine levels during long-term treatment (average, 20 months) than predicted; none had a faster rise than predicted. Seven of the 17 patients began treatment before creatinine reached the level of 8 mg per deciliter; in six of the seven, followed for an average of 22 months, creatinine has remained at or below the level at the start of treatment. Nutrition, as assessed by body weight, nitrogen balance, serum albumin, and serum transferrin, has been well maintained. This regimen slowed or arrested the rise in creatinine levels and thus must have slowed or halted the progression of renal insufficiency in a majority of cases, especially when treatment was initiated before creatinine had reached the level of 8 mg per deciliter. The mechanism underlying this effect remains to be determined.

Supplements containing amino acids and keto acids in the treatment of chronic uremia

Three mixtures containing varying proportions of threonine, tyrosine, and the ornithine, lysine, and histidine salts of branched-chain keto acids have been tested as dietary supplements to a 20- to 25-g mixed-quality protein diet in patients with severe chronic uremia. Two of the three supplements improved the abnormalities of plasma amino acid concentrations, and slowed or arrested progression of renal insufficiency. The second supplement, which contained less threonine and lysine, led to subnormal plasma concentrations of these two amino acids and aggravated hypophosphatemia. The third supplement, which also contained a small amount of the hydroxy analogue of methionine, was the most effective in slowing progression. The results emphasize the importance of optimizing the composition of such supplements.