Glucose and amino acid metabolism in chronic renal failure: effect of insulin and amino acids

Diabetes mellitus in dialysis and renal transplantation

Diabetes mellitus is the commonest cause of end-stage kidney failure worldwide and is a proven and significant risk factor for the development of cardiovascular disease. Renal impairment has a significant impact on the physiology of glucose homeostasis as it reduces tissue sensitivity to insulin and reduces insulin clearance. Renal replacement therapy itself affects glucose control: peritoneal dialysis may induce hyperglycaemia due to glucose-rich dialysate and haemodialysis often causes hypoglycaemia due to the relatively low concentration of glucose in the dialysate. Autonomic neuropathy which is common in chronic kidney disease (CKD) and diabetes increases the risk for asymptomatic hypoglycaemia. Pharmacological options for improving glycaemic control are limited due to alterations to drug metabolism. Impaired glucose tolerance and diabetes are also common in the post-kidney-transplant setting and increase the risk of graft failure and mortality. This review seeks to summarise the literature and tackle the intricacies of glycaemic management in patients with CKD who are either on maintenance haemodialysis or have received a kidney transplant. It outlines changes to glycaemic targets, monitoring of glycaemic control, the use of oral hypoglycaemic agents, the management of severe hyperglycaemia in dialysis and kidney transplantation patients.

How to Overcome Anabolic Resistance in Dialysis-Treated Patients?

A current hypothesis is that dialysis-treated patients are "anabolic resistant" i. e., their muscle protein synthesis (MPS) response to anabolic stimuli is blunted, an effect which leads to muscle wasting and poor physical performance in aging and in several chronic diseases. The importance of maintaining muscle mass and MPS is often neglected in dialysis-treated patients; better than to describe mechanisms leading to energy-protein wasting, the aim of this narrative review is to suggest possible strategies to overcome anabolic resistance in this patient's category. Food intake, in particular dietary protein, and physical activity, are the two major anabolic stimuli. Unfortunately, dialysis patients are often aged and have a sedentary behavior, all conditions which per se may induce a state of "anabolic resistance." In addition, patients on dialysis are exposed to amino acid or protein deprivation during the dialysis sessions. Unfortunately, the optimal amount and formula of protein/amino acid composition in supplements to maximixe MPS is still unknown in dialysis patients. In young healthy subjects, 20 g whey protein maximally stimulate MPS. However, recent observations suggest that dialysis patients need greater amounts of proteins than healthy subjects to maximally stimulate MPS. Since unneccesary amounts of amino acids could stimulate ureagenesis, toxins and acid production, it is urgent to obtain information on the optimal dose of proteins or amino acids/ketoacids to maximize MPS in this patients' population. In the meantime, the issue of maintaining muscle mass and function in dialysis-treated CKD patients needs not to be overlooked by the kidney community.

Accelerated whole-body protein catabolism in subjects with type 2 Diabetes Mellitus and albuminuria

Background

Albuminuria develops in ~40% of subjects with Type 2 Diabetes Mellitus (T2DM), and is often associated with malnutrition, severe comorbidities and decreased life expectancy. The association between albuminuria and altered whole body protein turnover in T2DM is currently unknown.

Objective

To assess whole body protein degradation and synthesis in type 2 diabetes with and without albuminuria.

Methods

Fourteen T2DM male subjects, with either increased [AER+] or normal [AER-] urinary albumin excretion rate, and eleven age-matched male healthy controls, were infused with phenylalanine [Phe] and tyrosine [Tyr] tracers. Post-absorptive rates of appearance (Ra) of Phe (= protein degradation) and Tyr, Phe hydroxylation to Tyr (Hy) (catabolic pathway), and Phe disposal to protein synthesis [PS], were determined.

Results

Phe and Tyr Ra were not different among the groups. However, in T2DM [AER+], the fraction of Phe disposal to hydroxylation was ~50% and ~25% greater than that of both controls and T2DM [AER-] (p<0.006 and p = 0.17, respectively). Conversely, as compared to controls, the fractional Phe disposal to PS was ~10% lower in T2DM [AER+] (p<0.006), and not different from that in T2DM [AER-]. As a consequence, in T2DM [AER+], the ratio between the fractional Phe disposal to hydroxylation and that to PS was ~70% greater (p = 0.005) than that in healthy controls, whereas in the T2DM [AER-] this ratio was ~30% greater than in controls (p = 0.19).

Conclusions

On the basis of the kinetics of the essential amino acid phenylalanine, T2DM subjects with increased AER exhibit a catabolic pattern of whole body protein turnover.

Muscle Atrophy in Chronic Kidney Disease

The renal damage and loss of kidney function that characterize chronic kidney disease (CKD) cause several complex systemic alterations that affect muscular homeostasis, leading to loss of muscle mass and, ultimately, to muscle atrophy. CKD-induced muscle atrophy is highly prevalent and, in association with common CKD comorbidities, is responsible for the reduction of physical capacity, functional independence, and an increase in the number of hospitalizations and mortality rates. Thus, this chapter summarizes current knowledge about the complex interactions between CKD factors and the pathophysiological mechanisms that induce muscle atrophy that, despite growing interest, are not yet fully understood. The current treatments of CKD-induced muscle atrophy are multidisciplinary, including correction of metabolic acidosis, nutritional supplementation, reducing insulin resistance, administration of androgenic steroids, resisted and aerobic exercise, neuromuscular electrical stimulation, and inspiratory muscle training. However, further studies are still needed to strengthen the comprehension of CKD-induced muscle atrophy and the better treatment strategies.

Dietary Intake of Proteins and Calories Is Inversely Associated With The Oxidation State of Plasma Thiols in End-Stage Renal Disease Patients

OBJECTIVES

Oxidative stress contributes to the pathogenesis of protein-energy wasting in maintenance hemodialysis (MHD) patients, but knowledge of specific effectors and mechanisms remains fragmented. Aim of the study was to define whether and how food intake is involved in the causal relationship between oxidative stress and protein-energy wasting.

METHODS

Seventy-one adult MHD patients and 24 healthy subjects (control) were studied cross-sectionally with analyses of diet record and of oxidative stress, as measured by a battery of plasma thiols including the protein sulfhydryl (-SH) group (PSH) levels (a marker of total protein-SH reducing capacity), the protein thiolation index (PTI, the ratio between disulfide, i.e., oxidized and reduced -SH groups in proteins), low molecular mass (LMM) thiols, LMM disulfides, and mixed LMM-protein disulfides. In addition, interleukin-6 (IL-6), albumin, C-reactive protein, and neutrophil gelatinase-associated lipocalin (NGAL) were measured as markers of inflammation.

RESULTS

The patients showed low energy (22.0 ± 8.4 kcal/kg/day) and adequate protein (1.0 ± 0.4 g/kg/day) intakes, high levels of cystine (CySS; patients vs.

CONTROL

113.5 [90.9-132.8] vs. 68.2 [56.2-75.7] μM), cysteinylated proteins (CySSP; 216.0 [182.8-254.0] vs. 163.5 [150.0-195.5] μM), and high PTI (0.76 [0.61-0.88] vs. 0.43 [0.40-0.54]; P < .001 in all comparisons). In patients, variation of CySSP was explained by a standard regression model (R = 0.775; P = .00001) that included significant contributions of protein intake (β = -0.361), NGAL (β = 0.387), age (β = 0.295), and albumin (β = 0.457). In the same model, variation of PTI (R = 0.624; P = .01) was explained by protein intake (β = -0.384) and age (β = 0.326) and NGAL (β = 0.311). However, when PSH was entered as dependent variable (R = 0.730; P = .0001), only serum albumin (β = 0.495) and age (β = -0.280), but not dietary intake or NGAL, contributed to the model.

CONCLUSIONS

In MHD, markers of thiol oxidation including CySSP and PTI show independent association with dietary intake and NGAL, whereas PSH, a marker of thiol-reducing capacity, did not associate with these same variables. The mechanism(s) responsible for inverse association between oxidative stress and food intake in MHD remain undefined.

Mechanisms of muscle wasting in chronic kidney disease

In patients with chronic kidney disease (CKD), loss of cellular proteins increases the risks of morbidity and mortality. Persistence of muscle protein catabolism in CKD results in striking losses of muscle proteins as whole-body protein turnover is great; even small but persistent imbalances between protein synthesis and degradation cause substantial protein loss. No reliable methods to prevent CKD-induced muscle wasting currently exist, but mechanisms that control cellular protein turnover have been identified, suggesting that therapeutic strategies will be developed to suppress or block protein loss. Catabolic pathways that cause protein wasting include activation of the ubiquitin-proteasome system (UPS), caspase-3, lysosomes and myostatin (a negative regulator of skeletal muscle growth). These pathways can be initiated by complications associated with CKD, such as metabolic acidosis, defective insulin signalling, inflammation, increased angiotensin II levels, abnormal appetite regulation and impaired microRNA responses. Inflammation stimulates cellular signalling pathways that activate myostatin, which accelerates UPS-mediated catabolism. Blocking this pathway can prevent loss of muscle proteins. Myostatin inhibition could yield new therapeutic directions for blocking muscle protein wasting in CKD or disorders associated with its complications.

Regulation of muscle protein synthesis and the effects of catabolic states

Protein synthesis and degradation are dynamically regulated processes that act in concert to control the accretion or loss of muscle mass. The present article focuses on the mechanisms involved in the impairment of protein synthesis that are associated with skeletal muscle atrophy. The vast majority of mechanisms known to regulate protein synthesis involve modulation of the initiation phase of mRNA translation, which comprises a series of reactions that result in the binding of initiator methionyl-tRNAi and mRNA to the 40S ribosomal subunit. The function of the proteins involved in both events has been shown to be repressed under atrophic conditions such as sepsis, cachexia, chronic kidney disease, sarcopenia, and disuse atrophy. The basis for the inhibition of protein synthesis under such conditions is likely to be multifactorial and includes insulin/insulin-like growth factor 1 resistance, pro-inflammatory cytokine expression, malnutrition, corticosteroids, and/or physical inactivity. The present article provides an overview of the existing literature regarding mechanisms and signaling pathways involved in the regulation of mRNA translation as they apply to skeletal muscle wasting, as well as the efficacy of potential clinical interventions such as nutrition and exercise in the maintenance of skeletal muscle protein synthesis under atrophic conditions. This article is part of a Directed Issue entitled: Molecular basis of muscle wasting.

Insulin resistance and protein metabolism in chronic hemodialysis patients

OBJECTIVE

Loss of lean body mass (sarcopenia) is associated with increased morbidity and mortality in patients receiving chronic hemodialysis (CHD). Insulin resistance (IR), which is highly prevalent in patients receiving CHD, has been proposed to play a critical role in the development of sarcopenia. The aim of this study was to examine the effect of IR on amino acid metabolism in patients receiving CHD.

DESIGN

This was a cross-sectional study.

SUBJECTS

The study included 12 prevalent (i.e., patients that have been on dialysis for more than 90 days) African American patients receiving CHD.

METHODS

IR was measured as glucose disposal rate (GDR) determined from hyperinsulinemic euglycemic clamp (HGEC) studies performed 3 consecutive times. Plasma amino acid (AA) concentrations were measured by real-time high-performance liquid chromatography (HPLC) throughout the clamp study. The primary outcome was percentage change in leucine concentrations during the clamp study. The main predictor was the GDR measured simultaneously during the HGEC studies. Mixed model analysis was used to account for repeated measures.

RESULTS

All individual AA concentrations declined significantly in response to high-dose insulin administration (P < .001). There was a significant direct association between GDR by HECG studies and the percentage change in leucine concentration (P = .02). Although positive correlations were observed between GDR values and concentration changes from baseline for other AAs, these associations did not reach statistical significance.

CONCLUSIONS

Our results suggest that the severity of IR of carbohydrate metabolism is associated with a lesser decline in plasma leucine concentrations, suggesting a similar resistance to protein anabolism. Insulin resistance represents a potential mechanism for sarcopenia commonly observed in patients receiving CHD.

The effect of dialysis membrane flux on amino acid loss in hemodialysis patients

We examined whether high flux membranes (HF) may induce a greater loss of amino acids compared to low flux membranes (LF). Ten hemodialysis patients participated in this study. Pre- and post-hemodialysis plasma amino acid profiles were measured by reverse-phase high pressure liquid chromatography for both HF and LF. We measured the dialysate amino acid losses during hemodialysis. The reduction difference for plasma total amino acid (TAA), essential amino acid (EAA), and branch chained amino acid (BCAA) was not significantly different in comparisons between the two membranes. (HF vs. LF; TAA 66.85 +/- 30.56 vs. 53.78 +/- 41.28, p=0.12; EAA 14.79 +/-17.16 vs. 17.97 +/- 28.69, p=0.12; BCAA 2.21 +/- 6.08 vs. 4.16 +/- 10.98 mg/L, p=0.13). For the HF, the reduction in plasma amino acid levels for TAA and EAA were statistically significant. Although it was not statistically significant, the dialysate losses of BCAA were greater than the reduction in plasma (plasma reduction vs. dialysate loss; HF 2.21 +/- 6.08 vs. 6.58 +/- 4.32, LF 4.16 +/- 10.98 vs. 7.96 +/- 3.25 mg/L). HF with large pores and a sieving coefficient do not influence dialysate amino acid losses. Hemodialysis itself may influence the dialysate amino acid losses and may have an effect on protein metabolism.

Amino acid repletion does not decrease muscle protein catabolism during hemodialysis

Intradialytic protein catabolism is attributed to loss of amino acids in the dialysate. We investigated the effect of amino acid infusion during hemodialysis (HD) on muscle protein turnover and amino acid transport kinetics by using stable isotopes of phenylalanine, leucine, and lysine in eight patients with end-stage renal disease (ESRD). Subjects were studied at baseline (pre-HD), 2 h of HD without amino acid infusion (HD-O), and 2 h of HD with amino acid infusion (HD+AA). Amino acid depletion during HD-O augmented the outward transport of amino acids from muscle into the vein. Increased delivery of amino acids to the leg during HD+AA facilitated the transport of amino acids from the artery into the intracellular compartment. Increase in muscle protein breakdown was more than the increase in synthesis during HD-O (46.7 vs. 22.3%, P < 0.001). Net balance (nmol.min(-1).100 ml (-1)) was more negative during HD-O compared with pre-HD (-33.7 +/- 1.5 vs. -6.0 +/- 2.3, P < 0.001). Despite an abundant supply of amino acids, the net balance (-16.9 +/- 1.8) did not switch from net release to net uptake. HD+AA induced a proportional increase in muscle protein synthesis and catabolism. Branched chain amino acid catabolism increased significantly from baseline during HD-O and did not decrease during HD+AA. Protein synthesis efficiency, the fraction of amino acid in the intracellular pool that is utilized for muscle protein synthesis decreased from 42.1% pre-HD to 33.7 and 32.6% during HD-O and HD+AA, respectively (P < 0.01). Thus amino acid repletion during HD increased muscle protein synthesis but did not decrease muscle protein breakdown.

Skeletal muscle dysfunction in chronic renal failure: effects of exercise

A number of chronic illnesses such as renal failure (CRF), obstructive pulmonary disease, and congestive heart failure result in a significant decrease in exercise tolerance. There is an increasing awareness that prescribed exercise, designed to restore some level of physical performance and quality of life, can be beneficial in these conditions. In CRF patients, muscle function can be affected by a number of direct and indirect mechanisms caused by renal disease as well as various treatment modalities. The aims of this review are twofold: first, to briefly discuss the mechanisms by which CRF negatively impacts skeletal muscle and, therefore, exercise capacity, and, second, to discuss the available data on the effects of programmed exercise on muscle function, exercise capacity, and various other parameters in CRF.

Coordinated increase in albumin, fibrinogen, and muscle protein synthesis during hemodialysis: role of cytokines

Serum albumin, fibrinogen levels, and lean body mass are important predictors of outcome in end-stage renal disease (ESRD). We estimated the fractional synthesis rates of albumin (FSR-A), fibrinogen (FSR-F), and muscle protein (FSR-M) in nine ESRD patients and eight controls, using primed constant infusion of l-[ring-(13)C(6)]phenylalanine. Cytokine profile and arteriovenous balance of amino acids were also measured. ESRD patients were studied before (Pre-HD) and during hemodialysis (HD). Plasma IL-6, IL-10, and C-reactive protein increased significantly during HD. Despite a decrease in the delivery of amino acids to the leg, the outflow of the amino acids increased during HD. The net balance of amino acids became more negative during HD, indicating release from the muscle. HD increased leg muscle protein synthesis (45%) and catabolism (108%) but decreased whole body proteolysis (15%). FSR-A during HD (9.7 +/- 0.9%/day) was higher than pre-HD (6.5 +/- 0.9%/day) and controls (5.8 +/- 0.5%/day, P < 0.01). FSR-F increased during HD (19.7 +/- 2.6%/day vs. 11.8 +/- 0.6%/day, P < 0.01), but it was not significantly different from that of controls (14.4 +/- 1.4%/day). FSR-M intradialysis (1.77 +/- 0.19%/day) was higher than pre-HD (1.21 +/- 0.25%/day) and controls (1.30 +/- 0.32%/day, P < 0.001). Pre-HD FSR-A, FSR-F, and FSR-M values were comparable to those of controls. There was a significant and positive correlation between plasma IL-6 and the FSRs. Thus, in ESRD patients without metabolic acidosis, the fractional synthesis rates of albumin, fibrinogen, and muscle protein are not decreased pre-HD. However, HD increases the synthesis of albumin, fibrinogen, and muscle protein. The coordinated increase in the FSRs is facilitated by constant delivery of amino acids derived from the muscle catabolism and intradialytic increase in IL-6.

Derangement of glucose metabolism in hyperparathyroidism

The derangement of glucose metabolism is found frequently in all forms of hyperparathyroidism. Both in primary (PHPT) and secondary hyperparathyroidism (SHPT) PTH excess is thought to be involved in deteriorating insulin sensitivity and secretion though their different clinical and pathophysiological conditions. In PHPT these abnormalities are related to a high frequency of Type 2 diabetes mellitus and also impaired glucose tolerance according to recent clinical studies, without differences between symptomatic and asymptomatic clinical presentation. In chronic renal failure (CRF), the disorders of glucose metabolism due to SHPT do not bear an increased risk for diabetes whereas they seem to be involved in the progression of atherosclerotic vascular damage which connotes CRF. Moreover, clinical and experimental studies have shown that vitamin D deficiency associated with glucose metabolism abnormalities favors the development of the metabolic syndrome. The potential for metabolic and cardiovascular harm related to hyperparathyroidism, especially PHPT, is the most interesting issue for clinical endocrinologists. This short review of the clinical and pathophysiological data of literature on glucose homeostasis disorders in hyperparathyroidism focuses on its potential clinical and therapeutic impact, particularly in the management of PHPT.

Resting energy expenditure in pre-dialysis diabetic patients

BACKGROUND

The metabolic derangements of diabetes mellitus (DM) associated with those of chronic renal failure (CRF) may interfere with the energy and protein balance of patients with both diseases. The aim of this study was to verify whether the resting energy expenditure (REE) of non-dialysis chronic renal failure diabetic patients differs from that of chronic renal failure patients without DM.

METHODS

REE was measured by indirect calorimetry in 24 CRF diabetic patients (CRF diabetes group), matched for age, gender, and degree of renal impairment to 24 CRF patients without DM (CRF control group).

RESULTS

The CRF diabetes group had a significantly higher REE (1538+/-230 kcal/day) than the CRF control group (1339+/-315 kcal/day, P = 0.009). This difference was maintained even when the REE was adjusted for lean body mass (LBM; 30.3+/-4.3 vs 26.3+/-5.4 kcal/kg LBM/day, P = 0.004). Mean protein intake was significantly higher in the CRF diabetes than in the CRF control group (0.89+/-0.20 vs 0.76+/-0.25 g/kg/day, P = 0.02). Mean protein equivalent of nitrogen appearance (PNA) was also significantly higher in the CRF diabetes patients (1.21+/-0.31 vs 1.03+/-0.22 g/kg/day, P = 0.02), reflecting a higher protein intake and/or elevated protein breakdown. Accordingly, REE was directly correlated with PNA mainly in the CRF diabetes group (r = 0.57, P < 0.003).

CONCLUSION

Metabolic disturbances of poorly controlled DM may account for the higher REE observed in the CRF diabetes group. The role of the apparently higher protein breakdown in this increased REE remains to be clarified.

Metabolic effects of restoring partial beta-cell function after islet allotransplantation in type 1 diabetic patients

Successful intraportal islet transplantation normalizes glucose metabolism in diabetic humans. To date, full function is not routinely achieved after islet transplantation in humans, with most grafts being characterized by only partial function. Moreover, the duration of full function is variable and cannot be sufficiently predicted with available methods. In contrast, most grafts retain partial function for a long time. We hypothesized that partial function can restore normal protein and lipid metabolism in diabetic individuals. We studied 45 diabetic patients after islet transplantation. Labeled glucose and leucine were infused to assess whole-body glucose and protein turnover in 1) 6 type 1 diabetic patients with full function after intraportal islet transplantation (FF group; C-peptide > 0.6 nmol/l; daily insulin dosage 0.03 +/- 0.02 U x kg(-1) body wt x day(-1); fasting plasma glucose < 7.7 mmol/l; HbA1c < or = 6.5%), 2) 17 patients with partial function (PF group; C-peptide > 0.16 nmol/l; insulin dosage < 0.4 U x kg(-1) body wt x day(-1)), 3) 9 patients with no function (NF group; C-peptide < 0.16 nmol/l; insulin dosage > 0.4 U x kg(-1) body wt x day(-1)), and 4) 6 patients with chronic uveitis as control subjects (CU group). Hepatic albumin synthesis was assessed in an additional five PF and five healthy volunteers by means of a primed-continuous infusion of [3,3,3-2H3]leucine. The insulin requirement was 97% lower than pretransplant levels for the FF group and 57% lower than pretransplant levels for the PF group. In the basal state, the PF group had a plasma glucose concentration slightly higher than that of the FF (P = 0.249) and CU groups (P = 0.08), but was improved with respect to the NF group (P < 0.01). Plasma leucine (101.1 +/- 5.9 micromol/l) and branched-chain amino acids (337.6 +/- 16.6 micromol/l) were similar in the PF, FF, and CU groups, and significantly lower than in the NF group (P < 0.01). During insulin infusion, the metabolic clearance rate of glucose was defective in the NF group versus in the other groups (P < 0.01). Both the basal and insulin-stimulated proteolytic and proteosynthetic rates were comparable in the PF, FF, and CU groups, but significantly higher in the NF group (P = 0.05). In addition, the PF group had a normal hepatic albumin synthesis. Plasma free fatty acid concentrations in the PF and FF groups were similar to those of the CU group, but the NF group showed a reduced insulin-dependent suppression during the clamp. We concluded that the restoration of approximately 60% of endogenous insulin secretion is capable of normalizing the alterations of protein and lipid metabolism in type 1 diabetic kidney recipients, notwithstanding chronic immunosuppressive therapy. The results of the present study indicate that "success" of islet transplantation may be best defined by a number of metabolic criteria, not just glucose concentration/metabolism alone.

Comparison of plasma amino acid concentrations in end-stage renal disease patients on hemodialysis and peritoneal dialysis

OBJECTIVES

Recent reports have suggested that patients treated by CAPD have a relatively increased risk of death compared to patients undergoing HD, although the cause of this discrepancy is poorly understood. Protein malnutrition is an important risk factor in ESRD. Also, amino acid concentrations, for which the physiological function differs from that of protein, may be an independent risk factor in ESRD. There is no doubt concerning the prevalence of low amino acid levels in both HD and CAPD patients. But the difference in plasma amino acid levels between these two groups has not been well defined. The purpose of this study is to compare plasma amino acid levels between patients with ESRD on HD and CAPD.

METHODS

A cross sectional study of overnight fasting plasma amino acid concentrations was performed on 12 CAPD and 45 HD patients with ESRD, matched by age, sex and body mass index. The levels of individual plasma amino acid and TAA, EAA, NEAA and BCAA were compared for the HD and CAPD groups. In order to measure losses during HD and CAPD, amino acid and protein concentrations were measured from 10 dialysates obtained from 10 HD patients and 12 peritoneal dialysis solutions from 12 CAPD patients.

RESULTS

All of the measured amino acid concentrations were found to be lower in the CAPD group compared to the HD group. Furthermore, the levels of TAA (2017.3 +/- 781.1 vs. 903.3 +/- 316.1 mumole/L), EAA(1201.8 +/- 492.6 vs. 567.6 +/- 223.2 mumole/L), NEAA(815.5 +/- 308.6 vs. 335.7 +/- 100.2 mumole/L); and BCAA (315.0 +/- 146.0 vs. 145.2 +/- 65.0 mumole/L), were all lower in the CAPD group than in the HD group. The protein loss was 2.0 +/- 0.2 g/L in the peritoneal dialysate but was not detectable in the hemodialysates. TAA loss over a one week period was about 61.8 +/- 13.0mmole for the HD group and 38.0 +/- 13.0 mmole for the CAPD group.

CONCLUSIONS

Our results show that amino acid concentrations are lower in ESRD patients on CAPD than on HD. It seems likely that protein loss in the peritoneal dialysate is a contributing factor to lowered plasma amino acid concentrations in ESRD patients on CAPD than on HD. We believe that the lowered amino acid concentrations observed in CAPD patients may worsen the clinical outcome compared to HD patients.

Metabolic effects of liver transplantation in cirrhotic patients

To assess whether liver transplantation (LTx) can correct the metabolic alterations of chronic liver disease, 14 patients (LTx-5) were studied 5+/-1 mo after LTx, 9 patients (LTx-13) 13+/-1 mo after LTx, and 10 patients (LTx-26) 26+/-2 months after LTx. Subjects with chronic uveitis (CU) and healthy volunteers (CON) were also studied. Basal plasma leucine and branched-chain amino acids were reduced in LTx-5, LTx-13, and LTx-26 when compared with CU and CON (P < 0.01). The basal free fatty acids (FFA) were reduced in LTx-26 with respect to CON (P < 0.01). To assess protein metabolism, LTx-5, LTx-13, and LTx-26 were studied with the [1-14C]leucine turnover combined with a 40-mU/m2 per min insulin clamp. To relate changes in FFA metabolism to glucose metabolism, eight LTx-26 were studied with the [1-14C]palmitate and [3-3H]glucose turnovers combined with a two-step (8 and 40 mU/m2 per min) euglycemic insulin clamp. In the postabsorptive state, LTx-5 had lower endogenous leucine flux (ELF) (P < 0.005), lower leucine oxidation (LO) (P < 0.004), and lower non-oxidative leucine disposal (NOLD) (P < 0.03) with respect to CON (primary pool model). At 2 yr (LTx-26) both ELF (P < 0.001 vs. LTx-5) and NOLD (P < 0.01 vs. LTx-5) were normalized, but not LO (P < 0.001 vs. CON) (primary and reciprocal pool models). Suppression of ELF by insulin (delta-reduction) was impaired in LTx-5 and LTx-13 when compared with CU and CON (P < 0.01), but normalized in LTx-26 (P < 0.004 vs. LTx-5 and P = 0.3 vs. CON). The basal FFA turnover rate was decreased in LTx-26 (P < 0.01) and CU (P < 0.02) vs. CON. LTx-26 showed a lower FFA oxidation rate than CON (P < 0.02). Tissue glucose disposal was impaired in LTx-5 (P < 0.005) and LTx-13 (P < 0.03), but not in LTx-26 when compared to CON. LTx-26 had normal basal and insulin-modulated endogenous glucose production. In conclusion, LTx have impaired insulin-stimulated glucose, FFA, and protein metabolism 5 mo after surgery. Follow-up at 26 mo results in (a) normalization of insulin-dependent glucose metabolism, most likely related to the reduction of prednisone dose, and, (b) maintenance of some alterations in leucine and FFA metabolism, probably related to the functional denervation of the graft and to the immunosuppressive treatment.

Kidney, splanchnic, and leg protein turnover in humans. Insight from leucine and phenylalanine kinetics

The rate of kidney protein turnover in humans is not known. To this aim, we have measured kidney protein synthesis and degradation in postabsorptive humans using the arterio-venous catheterization technique combined with 14C-leucine, 15N-leucine, and 3H-phenylalanine tracer infusions. These measurements were compared with those obtained across the splanchnic bed, the legs (approximately muscle) and in the whole body. In the kidneys, protein balance was negative, as the rate of leucine release from protein degradation (16.8 +/- 5.1 mumol/min.1.73 m2) was greater (P < 0.02) than its uptake into protein synthesis (11.6 +/- 5.1 mumol/min. 1.73 m2). Splanchnic net protein balance was approximately 0 since leucine from protein degradation (32.1 +/- 9.9 mumol/min. 1.73 m2) and leucine into protein synthesis (30.8 +/- 11.5 mumol/min. 1.73 m2) were not different. In the legs, degradation exceeded synthesis (27.4 +/- 6.6 vs. 20.3 +/- 6.5 mumol/min. 1.73 m2, P < 0.02). The kidneys extracted alpha-ketoisocaproic acid, accounting for approximately 70% of net splanchnic alpha-ketoisocaproic acid release. The contributions by the kidneys to whole-body leucine rate of appearance, utilization for protein synthesis, and oxidation were approximately 11%, approximately 10%, and approximately 26%, respectively; those by the splanchnic area approximately 22%, approximately 27%, and approximately 18%; those from estimated total skeletal muscle approximately 37%, approximately 34%, and approximately 48%. Estimated fractional protein synthetic rates were approximately 42%/d in the kidneys, approximately 12% in the splanchnic area, and approximately 1.5% in muscle. This study reports the first estimates of kidney protein synthesis and degradation in humans, also in comparison with those measured in the splanchnic area, the legs, and the whole-body.