Impaired glucose oxidation and glucose-induced thermogenesis in renal transplant recipients

Emanuela de Pascale1, Mauro Giordano1, Matilde Carone2, Corrado Pluvio2, Maria Pluvio2, Tullio Criscuolo3, Lorena Infantone1 and Pietro Castellino1,

1 Istituto di Clinica Medica Generale e Terapia Medica ‘L. Condorelli’ Universita' di Catania, 2 Istituto di Medicina Interna e Nefrologia e 3 Istituto di Endocrinologia, Seconda Universita' di Napoli, Italy



   Abstract
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
Background. Renal transplant recipients often show various metabolic abnormalities including reduced glucose tolerance, impaired insulin sensitivity and altered lipid metabolism. However, the acute effects of carbohydrate ingestion on substrate utilization and energy expenditure have not been fully elucidated.

Methods. We evaluated: (i) basal energy expenditure (EE) and substrate utilization, (ii) metabolic fate of an oral glucose load, and (iii) substrate-induced thermogenesis in: (a) 15 non-diabetic renal transplant recipients (Tx) (BMI 25±1) on triple immunosuppressive therapy, (b) 11 patients with primary glomerulonephritis (BMI 25±1) (Cort) receiving prednisone treatment, and (c) 12 healthy subjects (BMI 26±1) (N). Continuous indirect calorimetry was performed in the basal post-absorptive state for 60 min and continued for an additional 180 min following an oral glucose load (75 g).

Results. In the basal state, EE was similar in the three study groups. It averaged 14.6±0.7, 15.7±1.3, and 14.1±0.8 cal/kg/min in Tx, Cort, and N respectively. Glucose oxidation was higher in N (1.3± 0.2 mg/kg/min) than in Tx (0.7±0.2) and Cort (1.0±0.2) (P<0.05 in N vs Tx and vs Cort), whereas lipid oxidation was lower in N (0.6±0.1 mg/kg/min) than in Tx (0.9±0.1) and Cort (0.9±0.05) (P<0.03 in N vs Tx and vs Cort). After glucose ingestion, total carbohydrate oxidation averaged 21.2±2, 31.0±3, and 29.6±3 g, which represented 28±3, 41±3 and 39±2% of the total glucose load in Tx, Cort and N respectively (P<0.01 Tx vs Cort and N). The cumulative increase of EE (180 min) was 9.7±2, 13.2±3 and 13±3 kcal in Tx, Cort, and N respectively.

Conclusions. The present data show that in non-diabetic renal transplant recipients basal EE is normal. However, basal lipid oxidation is higher and glucose oxidation is lower than in healthy subjects. In addition, the oxidative disposal of a glucose load and substrate-induced thermogenesis are impaired.

Keywords: glucose metabolism; thermogenesis; renal transplant recipients



   Introduction
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
Corticosteroids play a pivotal role in the clinical management of organ transplantation [1]. However, the metabolic abnormalities associated with their use represent a matter of concern. Glucose intolerance and weight gain have been described in as many as 40% of corticosteroid-treated transplant recipients [2,3] and contribute significantly to the overall morbidity of renal transplantation. Introduction of cyclosporin A (CsA) has allowed a reduction in daily and cumulative corticosteroid dose [4]. Nevertheless, between 10 and 15% of renal transplant recipients maintained on triple drug therapy will eventually develop post-transplant diabetes mellitus [5]. In addition, renal transplant recipients who do not develop post-transplant diabetes mellitus often show a reduced sensitivity to insulin and an impaired glucose tolerance [3,6]. In these patients little is known of substrate oxidation energy expenditure and thermogenic response to substrate ingestion. The present study was designed to evaluate in non-diabetic renal transplant recipients maintained on triple immunosuppressive drug therapy: (i) basal energy expenditure and substrate utilization, (ii) metabolic fate of an oral glucose load, and (iii) substrate-induced thermogenesis.



   Subjects and methods
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
Fifteen renal transplant recipients (Tx) (8 males/7 females, age 38±4 years, BMI 25±1 kg/m2, and IBW 107±3%) were enrolled in the study. Their immunosuppressive drug regimen included CsA (1.5–2.0 mg/kg/day), azathioprine (1 mg/kg/day), and prednisone (4–8 mg/day). Kidney transplant had been performed 58±6 months prior to the study. Eleven patients were on antihypertensive therapy; none was treated with thiazide or beta blockers. Ten patients had one transplant rejection episode and four patients had two rejection episodes, all treated with steroids, except one who was treated with monoclonal antibody OKT3. Initial dose of methylprednisolone was 10 mg/kg body weight (BW) for 3 days, progressively reduced over the 2 weeks following rejection episodes. None of the transplant recipients had a rejection episode within the 12 months prior to their participation in the study. There were two control groups: the ‘Cort’ group and the ‘N’ group. The Cort group consisted of 11 patients with primary glomerulonephritis (8 males, 3 females, age 31±3 years, BMI 25±1 kg/m2, IBW 106±3%). Biopsy-based diagnoses were four membranoproliferative, three mesangioproliferative, and four IgA nephropathy. Subjects were treated with steroids (0.5–1 mg/kg BW) and were currently under maintenance therapy with low-dose steroids (4–8 mg/day) for 12–24 months prior to the study. The N group consisted of 12 healthy normal subjects (5 males, 7 females, age 34±3 years, BMI 26±1 kg/m2, IBW 108±2%). All subjects consumed a diet that provided at least 200 g of carbohydrate and 0.9–1.1 g of protein per kg BW per day for at least 7 days prior to the study. Exclusion criteria were heart failure, endocrine diseases, plasma creatinine >1.5 mg/dl. The purpose and potential risks of the study were explained to all subjects and a voluntary consent was obtained prior to their participation.

Studies were performed at 08.00 hours after an overnight fast. The last medication was taken at least 12 h prior to the study. Continuous indirect calorimetry was performed for 60 min. At the end of the basal period an oral glucose load of 75 g was administered to all subjects. Continuous indirect calorimetry was continued for an additional 180 min following glucose ingestion. Blood samples were drawn at 30-min intervals throughout the entire study for substrate and hormone determinations. Twenty-four-hour urine collections for nitrogen excretion were performed the day before the study. Blood and urinary glucose levels were evaluated by the glucose oxidase method on a Beckman Glucose Analyzer II (Beckman Instruments, Fullerton, CA). Insulin levels were evaluated by standard radioimmunoassay methods. Oxygen consumption and carbon dioxide production were determined with a Deltatrac M 100 (Datex, Helsinki, Finland). Energy expenditure was calculated from calorimetric data using standard formulae [7]. Protein oxidation was evaluated from urinary nitrogen excretion. Its value was used to calculate non-protein oxygen consumption and carbon dioxide production. Glucose and lipid oxidation were derived from non-protein oxygen consumption and carbon dioxide production using standard formulae [7].

The amount of glucose stored during the test was calculated by subtracting the total rate of glucose oxidation from the total amount of administered glucose after correction for changes of mass of glucose in the glucose space. Calculations were based on the following assumptions: (i) gastrointestinal absorption of the ingested glucose >95%, and (ii) hepatic glucose production suppressed >90% following the glucose load [8]. Previous studies have not demonstrated a significant effect of immunosuppressive drugs on gastric emptying or intestinal glucose absorption [9,10]. The minimal theoretical cost of glucose storage was considered to be 0.2 kcal/g of glucose stored [11].

The degree of insulin resistance has been evaluated using the homeostasis model assessment (HOMA) as follows: IR=FIxG / 22.5; where IR is the rate of insulin resistance, FI is the concentration of fasting plasma insulin (µU/ml), and G is the concentration of fasting plasma glucose (mmol/l) [12]. During 180 min of the oral glucose tolerance test (OGTT) the sensitivity of glucose oxidation to insulin was calculated according to the formula: insulin mediated glucose oxidation during OGTT=total glucose oxidation (g)/mean plasma insulin level (µU/ml).

All values are expressed as means±SE. Comparisons between the basal and glucose administration periods were made using the t-test for paired data. Inter-group analysis was performed by one-way analysis of variance.



   Results
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 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
Plasma insulin and glucose levels (Figure 1Go)
Basal insulin levels averaged 18±2, 16±3, and 11±2 µU/ml in Tx, Cort and N respectively (P<0.05 Tx vs N). In response to glucose ingestion insulin levels rose significantly in all study groups (P<0.01 vs basal at all time points), and at 60 and 120 min insulin levels averaged 113±21 and 89±20 µU/ml in Tx, 92±16 and 69±10 µU/ml in Cort, and 70±11 and 45±8 µU/ml in normal subjects (P<0.03 Tx vs N at 60 min, and P<0.03 Tx vs N and Cort vs N at 120 and 180 min) (Figure 1Go). Basal plasma glucose levels were similar in the three study groups and averaged 79±2, 75±3, and 79±3 mg/dl in Tx, Cort, and N respectively; in response to the ingestion of 75 g of glucose, plasma glucose rose significantly in all groups and at 120 min averaged 116±6, 102±10, and 105±8 mg/dl in Tx, Cort, and N respectively (all P<0.01 vs basal, P=ns Tx vs Cort and vs N) (Figure 1Go). The HOMA index of insulin resistance were 3.51±0.28, 2.96±0.31, and 2.15±0.22, in Tx, Cort and N groups respectively (P<0.01 in N vs Tx and vs Cort).



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Fig. 1. Time course of plasma insulin (left panel) and glucose levels (right panel) after the oral glucose load in transplant recipients (full circles), in corticosteroid-treated subjects with glomerulonephritis (open circles), and in normal subjects (open squares). Values are mean±SEM. *P<0.03 Tx vs N at 60 min, and P<0.03 Tx vs N and Cort vs N at 120 and 180 min.

 

Substrate utilization and energy expenditure (Figures 2Go and 3Go)
Basal energy expenditure (EE) was similar in the three study groups and averaged 14.6±0.7, 15.7±1.3, and 14.1±0.8 cal/kg/min in Tx, Cort, and N respectively (Figure 2Go). In the basal state, the non-protein respiratory quotient was significantly higher in N (0.85±0.03) than in Tx (0.78±0.03) and Cort (0.77±0.03) (P<0.03 N vs Tx and vs Cort). Basal glucose oxidation was higher in normal subjects (1.3±0.2 mg/kg/min) than in Tx (0.7±0.2) and Cort (1.0±0.2) (P<0.05 N vs Tx and vs Cort). In contrast, lipid oxidation was lower in normal subjects (0.6±0.1 mg/kg/min) than in Tx (0.9±0.1) and Cort (0.9±0.05) (P<0.03 N vs Tx and vs Cort) (Figure 2Go). Protein oxidation reflected dietary protein intake and was 0.68±0.06, 0.73±0.07, and 0.76±0.05 mg/kg/min in Tx, Cort, and N groups respectively. In the 180 min after the 75-g oral glucose load the cumulative rate of carbohydrate oxidation averaged 21.3±2, 31.0±3, and 29.6±3 g in Tx, Cort, and N respectively (P<0.01 Tx vs Cort and vs N) (Figure 3Go). These values represented 28±3, 41±3 and 39±2% of the total glucose load in Tx, Cort, and N respectively (P<0.01 Tx vs Cort and vs N). The indices of sensitivity of glucose oxidation to circulating insulin levels were 0.208±0.02, 0.368±0.04, and 0.539±0.05 in Tx, Cort and N respectively (P<0.01 Tx vs N). In response to the oral glucose load EE rose significantly to a peak of 16.5±0.6, 17.5±1.1, and 16.1±0.6 cal/kg/min in Tx, Cort, and N respectively (all P<0.01 vs basal). The cumulative increases of EE in the 180 min following the glucose load were 9.7±2, 13.2±3, and 13±3 kcal in Tx, Cort, and N. The minimum theoretical energy costs of storage as glycogen of the non-oxidized glucose were 10.2±1, 9.0±1, and 8.8±1 kcal in Tx, Cort, and N respectively.



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Fig. 2. Energy expenditure (upper left panel), non-protein respiratory quotient (NPRQ) (upper right panel), glucose oxidation (lower left panel) and lipid oxidation (lower right panel) during basal state in the three study groups. Values are mean±SEM. *P<0.03 N vs Tx and vs Cort.

 


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Fig. 3. Cumulative rate of glucose oxidation in the 180 min following oral glucose load in the three study groups. Values are mean±SEM. *P<0.01 Tx vs Cort and N.

 



   Discussion
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 
In the present study we investigated the post-absorptive rate of EE and substrate utilization as well as the metabolic response to an oral glucose load in renal transplant recipients with normal glucose tolerance. In these patients the use of both steroids and CsA can affect glucose and lipid metabolism [13]. In order to differentiate the effects of combined steroids and CsA therapy from those of steroids per se an additional control group of patients with primary glomerular diseases who were maintained on low-dose steroids as a single therapy was also studied. Tx patients showed a preferential utilization of lipids; basal and substrate-induced glucose oxidation were reduced. The rate of EE, as assessed by continuous indirect calorimetry, was similar in all study groups; however, the thermogenic response to glucose administration was reduced.

Mathieu et al. [14] reported a normal basal substrate utilization in transplant recipients maintained on CsA monotherapy. Preferential lipid utilization as energy source may therefore be ascribed to steroid administration. Increased triglyceride and free fatty acid (FFA) levels and lipoprotein lipase activity are dependent on circulatory levels of endogenous and exogenous corticosteroids [15]. Thus, the lower basal non-protein respiratory quotient (Figure 2Go) in the steroid-treated groups may be the metabolic consequence of the increased availability of lipids as an energy substrate. In addition, Mathieu et al. [14] reported an increase in transplant recipients in body fat content that may contribute to the enhanced FFA availability and utilization of lipids as energy source. In the present study transplant recipients and steroid-treated subjects had normal basal glucose levels and glucose tolerance. Nevertheless, they showed increased fasting insulin levels and marked hyperinsulinaemia in response to the oral glucose load (75 g). Modified HOMA indexes for glucose levels as well as for glucose oxidation were both consistent with a condition of insulin resistance that was partially compensated for by chronic fasting and postprandial hyperinsulinaemia [12]. Previous studies have shown that impaired peripheral glucose uptake may be due to altered glucose oxidation or to impaired storage of glucose as glycogen. These metabolic pathways are known to occur in muscle; thus the decline in lean body mass that characterizes Tx subjects [14,16] may contribute to pathway impairment.

In the present study we investigated the relative contribution of oxidative and non-oxidative pathways to the disposal of an oral glucose. We observed a 30–33% reduction in the oxidative disposal of glucose in Tx group in comparison with the normal subjects., Ekstrand et al. [6,17], using the euglycaemic insulin clamp technique, showed an impairment in non-oxidative glucose disposal and a reduction of glycogen synthase activity in non-diabetic renal transplant recipients. The present data do not allow exclusion of an impairment in non-oxidative glucose disposal under euglycaemic hyperinsulinaemia. Rather they provide evidence of an impairment in glucose oxidation in non-diabetic transplant recipients, which has not previously been described under euglycaemic hyperinsulinaemic conditions [6,17]. These discrepancies on the role of glucose oxidation in the utilization of a glucose load deserve further comment. They may be explained by the greater contribution of the splanchnic bed in the disposal of an oral glucose load (25%) in comparison with what occurs following i.v. glucose/insulin administration (10%) [18] and by the attendant portal hyperinsulinaemia and hyperglycaemia that follow the splanchnic absorption of the substrate [8,17]. Continuous indirect calorimetry allows an estimate of the thermogenic response to substrate administration. Following a glucose load, the observed rise in EE reflects the energy cost of glucose storage. The major metabolic pathway for glucose storage is glycogen synthesis. The energy cost of glycogen synthesis is estimated at 5.3% of the energy content of the glucose stored [11]. In N subjects and Cort groups we observed a glucose-induced rise in EE greater than the minimal theoretical cost of glucose storage as glycogen. The difference between the predicted and the observed rise in EE is ‘facultative’ thermogenesis. This is the consequence of various metabolic events induced by substrate administration such as glucose recycling through tricarbon compounds, lipogenesis, sodium-pump activity, catecholamine release and adrenergic sensitivity [5]. It is of interest that in Tx subjects no facultative thermogenesis was observed. Whether this phenomena is the consequence of CsA administration, antihypertensive treatment(s) or other as yet unidentified factors is unknown.

The present study demonstrates that subjects who do not develop post-transplant diabetes mellitus are nevertheless characterized by significant abnormalities in nutrient utilization. It is known that the incidence of post-transplant diabetes mellitus is highest within the first 24 months after transplantation. Therefore it may be of interest to evaluate the above-mentioned changes with a prospective approach.



   Notes
 
Correspondence and offprint requests to: Professor Pietro Castellino, Istituto di Clinica Medica Generale e Terapia Medica ‘L. Condorelli’, Via Plebiscito 628, I-95124 Catania, Italy. Back



   References
 Top
 Abstract
 Introduction
 Subjects and methods
 Results
 Discussion
 References
 

  1. Hricik DE, Almawi WY, Strom TB. Trends in the use of glucocorticoids in renal transplantation. Transplantation1994; 57: 979–989[ISI][Medline]
  2. Ruiz JO, Simmons RL, Callender CO, Kjellstrand CM, Buselmeier TJ, Najaran JS. Steroid diabetes in renal transplant recipients: pathogenic factors and prognosis. Surgery1973; 73: 759–765[ISI][Medline]
  3. Hjelmesaeth J, Hartmann A, Kofstad J et al. Glucose intolerance after renal transplantation depends upon prednisolone dose and recipient age. Transplantation1997; 64: 979–983[ISI][Medline]
  4. Ponticelli C, Civati G, Tarantino A et al. Randomized study with cyclosporine in kidney transplantation: 10-year follow up. J Am Soc Nephrol1996; 7: 792–797[Abstract]
  5. Miles AM Sumrani N, Horowitz R et al. Diabetes mellitus after renal transplantation: as deleterious non-transplant associated diabetes? Transplantation1998; 65: 380–384[ISI][Medline]
  6. Ekstrand A, Eriksson J, Gronhagen-Riska C, Ahonen P, Groop L. Insulin resistance and insulin deficiency in the pathogenesis of post transplantation diabetes in man. Transplantation1992; 53: 563–569[ISI][Medline]
  7. Simonson DC, DeFronzo RA. Indirect calorimetry: methodological and interpretative problems. Am J Physiol1990; 258: 399–412
  8. Ferrannini E, Bjorkman O, Reichard G et al. The disposal of an oral glucose load in healthy subjects. A quantitative study. Diabetes1985; 34: 580–588[Abstract]
  9. Dias VC, Madsen KL, Yatscoff RW, Doring K, Thomson AB. Orally administered immunosuppressants modify intestinal uptake of nutrients in rabbits. Transplantation1994; 58: 1241–1246[ISI][Medline]
  10. Markell MS, Armenti V, Danovitch G, Sumrani N. Hyperlipidemia and glucose intolerance in the post renal transplant patients. J Am Soc Nephrol1994; 4: S37–47[Abstract]
  11. Thiebaud D, Schutz Y, Acheson K et al. Energy cost of glucose storage in human subjects during glucose–insulin infusions. Am J Physiol1983; 244: E216–221[Abstract/Free Full Text]
  12. Matthews DR, Hosker JP, Rudenski AS, Naylor BA, Treacher DF, Turner RC. Homeostasis model assessment: insulin resistance and ß-cell function from fasting plasma glucose and insulin concentrations in man. Diabetologia1985, 28: 412–419[ISI][Medline]
  13. Jindal R. Post transplant diabetes mellitus: a review. Transplantation1994; 58: 1289–1298[ISI][Medline]
  14. Mathieu RL, Casez JP, Jaeger P, Montandon A, Peheim E, Horber FF. Altered body composition and fuel metabolism in stable kidney transplant patients on immune-suppressive monotherapy with cyclosporine A. Eur J Clin Invest1994; 24: 195–200[ISI][Medline]
  15. Ottosson M,Vikman-Adolfson K, Enerback S, Olivecrona G, Bjorntorp O. The effects of cortisol on the regulation of lipoprotein lipase activity in human adipose tissue. J Clin Endocrinol Metab1994; 79: 820–825[Abstract]
  16. Steiger U, Lippuner K, Jansen EX, Montandon A, Jaeger P, Horber FF. Body composition and fuel metabolism after kidney grafting. Eur J Clin Invest1995; 25: 809–816[ISI][Medline]
  17. Ekstrand A, Schalin-Jantti C, Lofman M et al. The effect of (steroid) immunosuppression on skeletal muscle glycogen metabolism in patients after kidney transplantation. Transplantation1996; 61: 889–893[ISI][Medline]
  18. Katz L, Glickman M, Rapoport S, Ferrannini E, DeFronzo RA. Splanchnic and peripheral disposal of oral glucose in man. Diabetes1983; 32: 675–679[Abstract]
Received for publication: 8.10.99
Revision received 18. 4.00.



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