Insulin resistance in uremia. Characterization of lipid metabolism in freshly isolated and primary cultures of hepatocytes from chronic uremic rats

Association between preoperative lipid profiles and new-onset diabetes after transplantation in Chinese kidney transplant recipients: A retrospective cohort study

Background

This study investigated the association between the preoperative lipid profiles and new‐onset diabetes after transplantation (NODAT) in Chinese kidney transplant recipients (KTRs).

Methods

In this study, of 1140 KTRs registered between January 1993 and March 2018 in Zhongshan Hospital, Fudan University, 449 were enrolled. Clinical data, obtained through a chart review of the patient records in the medical record system, were evaluated, and NODAT was diagnosed based on the American Diabetes Association guidelines. Multivariate Cox regression analysis was conducted to determine whether the preoperative lipid profiles in KTRs were independently associated with NODAT incidence. The preoperative lipid profiles were analyzed as continuous variables and grouped into tertiles. Smooth curve fitting was used to confirm the linear associations.

Results

During a median follow‐up of 28.03 (interquartile range 12.00–84.23) months, 104 of the 449 (23.16%) participants developed NODAT. The multivariate model analysis, adjusted for all potential covariates, showed that increased values of the following parameters were associated with NODAT (hazard ratio, 95% confidence interval): preoperative total cholesterol (TC; 1.25, 1.09–1.58, p = 0.0495), low‐density lipoprotein cholesterol (LDL‐C; 1.33, 1.02–1.75, p = 0.0352), non‐high‐density lipoprotein cholesterol (non‐HDL‐C; 1.41, 1.09–1.82, p = 0.0084), TC/HDL‐C (1.28, 1.06–1.54, p = 0.0109), and non‐HDL‐C/HDL‐C (1.26, 1.05–1.52, p = 0.0138). However, the association between the preoperative triglyceride, HDL‐C, or TG/HDL‐C and NODAT was not significant.

Conclusions

Preoperative TC, LDL‐C, non‐HDL‐C, TC/HDL‐C, and non‐HDL‐C/HDL‐C were independent risk factors for NODAT.

Morphological and functional differences in haemostatic axis between kidney transplanted and end-stage renal disease patients

End-stage renal disease (ESRD) is characterized by several atherothrombotic abnormalities, and kidney transplant seems to improve most of them. However, because it is not clear which mechanism is responsible for such improvement, our purpose was to clarify that point.We conducted a cross sectional study involving 30 ESRD patients, 30 ESRD kidney-transplanted patients (Ktx) and 30 healthy controls (C) to evaluate platelet morphology and function, atherothrombotic profile, endothelial abnormalities and cytokine levels involved in the insulin resistance/endothelial dysfunction. (i) Platelet morphology: The ESRD group showed platelet size similar to the other two groups (ESRD=3518x10(3)+/-549x10(3) nm2, C=3075x10(3)+/-197x10(3) nm2, Ktx=2862x10(3)+/-205x10(3) nm2) with similar platelet granules and number. (ii) Platelet surface glycoprotein: The CD41 and P-Selectin were similar between groups. (iii) Platelet intracellular calcium: Resting intracellular calcium was statistically higher in ESRD compared to the C group (ESRD=182.1+/-34.5, Ktx=126.7+/-14.1, C=72.0+/-11.0 nM, P<0.01). (iv) Hypercoagulability markers and natural anticoagulants: The Ktx and ESRD groups showed higher levels of hypercoagulability markers compared to the C group. A reduction in antithrombin activity was evident in ESRD compared to the Ktx group (P=0.03). (v) Endothelial morphology: The ESRD group showed a thickened vessel basal membrane compared to the Ktx and C groups with more endothelial sufference. (vi) Insulin resistance and pro-inflammatory cytokine profile: The ESRD showed a higher homeostasis model assessment provided equations for estimating insulin resistance (HOMA-IR) compared to the Ktx and C groups (ESRD=2.6+/-0.3, Ktx=1.8+/-0.2, C=1.1+/-0.1, P=0.005) and increased soluble tumor neurosis factor alpha (sTNFalpha) (P<0.05) and soluble vascular cell adhesion molecule (sVCAM) levels (P<0.01). Positive correlations were evident among HOMA-IR and sTNFalpha (P<0.001) and sVCAM (P=0.01), respectively. In a small subgroup of ESRD who underwent Ktx (five pts), our findings were confirmed at 1 year of follow-up, suggesting an improvement of almost haemostatic abnormalities. Kidney transplant is associated with a better atherothrombotic profile in ESRD, platelet intracellular calcium and cytokines seem to be most influenced by the transplant, while most morphological abnormalities are retained.

Lipogenic potential of liver from morbidly obese patients with and without non-insulin-dependent diabetes

Intra-abdominal liver biopsies were obtained during surgery from fasted obese patients with non-insulin-dependent diabetes mellitus (NIDDM), obese normoglycemic controls, and lean controls. Lipid synthesis was studied in freshly isolated hepatocytes and liver homogenates from the three groups of subjects. Incorporation of 3H2O into the lipids of hepatocytes was determined in the absence and presence of insulin (0.1 mumol/L). The activities of five enzymes involved in fatty acid synthesis, and the incorporation of 14C-glycerol-3-phosphate into lipids were determined in liver homogenates. Basal lipid synthesis by hepatocytes was not different in the three groups of patients. Insulin stimulated lipogenesis by 8% +/- 30% in the lean controls, 33% +/- 8% in the obese controls and 17% +/- 6% in the NIDDM patients. No significant differences in the activities of the five enzymes that are involved in de novo fatty acid synthesis among the three groups of patients were observed. Similarly, incorporation of 14C-glycerol-3-phosphate by liver homogenates, in the presence of saturating or submaximal concentrations of fatty acids, did not differ among the three groups. These results show that under the experimental conditions of this study, including the fasted state of the patients, the basal capacity of liver of NIDDM patients to synthesize fatty acids or glycerides is the same as that of liver from obese and lean controls. Thus, it is likely that an increase in fatty acid flux into a liver with normal lipogenic potential may contribute to the increased synthesis of triglycerides by the liver of these patients in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperlipidaemia in uraemic patients under chronic haemodialysis. Correlation with serum lipoprotein lipase and insulin levels

Hyperlipidaemia is implicated in vascular complications of uraemic patients on haemodialysis. In this work serum lipids, serum lipoprotein lipase (LPL) and insulin levels were measured in 45 chronic uraemic patients on haemodialysis and 44 healthy volunteers. A significant rise in total lipids (TL), cholesterol and triglycerides (TG) was detected in the haemodialysis patients, but no changes were found in either serum phospholipids or high density lipoprotein cholesterol (HDL-chol.). The rise in TL, TG and cholesterol was positively correlated with the duration of dialysis but not with age or sex. On the other hand, a significant rise was also observed in serum LPL and insulin levels but with no correlation between any of them and the lipid levels. From this study it may be apparent that other factors rather than LPL abnormalities may be implicated in hyperlipidaemia in uraemic patients under haemodialysis.

Insulin resistance of uremia

Glucose intolerance is a nearly universal finding in patients with chronic renal failure and in animal models of uremia. The glucose intolerance results from impaired insulin-mediated glucose disposal by muscle, adipose, and liver tissue. Insulin binding by these tissues is not reduced. Rather, several defects exist in the postreceptor cascade of insulin action. Although impaired insulin-mediated glucose uptake and metabolism occur, the primary defect and causative agent are not established. The purpose of the present article is to review recent literature on the potential mechanisms underlying the insulin resistance of chronic renal failure.

Alterations of glucose transporter systems in insulin-resistant uremic rats

To further define the cellular alteration(s) involved in the impaired glucose transport associated with chronic uremia, we examined the concentration and translocation of glucose transport systems in adipocytes isolated from partially nephrectomized uremic rats. Uremic animals, compared with matched controls, had increased blood urea nitrogen and serum insulin, whereas serum glucose was unchanged. In agreement with previous work, 125I-insulin binding to its receptor was unaltered and transport of 2-deoxy-D-glucose was decreased in both the absence (basal) and presence of a maximal (7 nM) insulin concentration by 44 and 35%, respectively. To assess the movement and concentration of glucose transport systems in various membrane fractions prepared from basal and insulin-treated (20 nM) uremic fat cells, the technique of D-glucose-inhibitable cytochalasin B binding was utilized. In plasma membranes isolated from these cells the concentration of glucose transporters was decreased by 16 (P less than 0.01) and 30% (P less than 0.005) in basal and insulin-treated cells, respectively. Concomitantly, microsomal membranes prepared from uremic cells treated in the absence and presence of insulin had a 28 (P less than 0.01) and 15% (P less than 0.05) decrease in concentration of glucose transport systems, respectively. Additionally, glucose transporter concentration was significantly decreased by 17% (P less than 0.025) in total membranes prepared from uremic cells. Thus, impairment of glucose transport in uremic fat cells can be attributed to a postbinding defect that, at least in part, results from a decrease in the total concentration of glucose transporters.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin resistance in uremia: insulin receptor kinase activity in liver and muscle from chronic uremic rats

We have studied the structure and function of the partially purified insulin receptors from liver and skeletal muscle in a rat model of severe chronic uremia. 125I-insulin binding was higher in the liver from uremic rats when compared with ad libitum- and pair-fed controls. Furthermore, the ability of insulin to stimulate the autophosphorylation of the beta-subunit and insulin receptor kinase activity using Glu80, Tyr20 as exogenous phosphoacceptor was increased in the liver of the uremic animals. The structural characteristic of the receptors, as determined by electrophoretic mobilities of affinity labeled alpha-subunit and the phosphorylated beta-subunit, were normal in uremia. 125I-insulin binding and insulin receptor kinase activity were similar in the skeletal muscle from uremic and pair- and ad libitum-fed animals. Thus our data are supportive of the hypothesis that in liver and muscle of chronic uremic rats, insulin resistance is due to a defect(s) distal to the insulin receptor kinase.

Insulin-like growth factor I binding in hepatocytes from human liver, human hepatoma, and normal, regenerating, and fetal rat liver

Insulin-like growth factor-I (IGF-I) in human hepatoma cells (HEP-G2) has, in addition to its effect on cell growth, short-term metabolic effects acting through its own receptor. We have demonstrated that normal human hepatocytes, compared with HEP-G2 cells, have virtually no IGF-I binding sites. Because the rate of growth is the major difference between the hepatoma and the normal liver, we asked if normal liver might express IGF-I binding sites under physiologic growth conditions. Indeed, whereas adult rat hepatocytes have low IGF-I binding sites similar to those in human liver, hepatocytes from regenerating liver after 3 d subtotal hepatectomy have an approximately sixfold increase (P less than 0.005) and those from fetal rat liver a approximately 12-fold increase (P less than 0.005), to levels comparable to those in the HEP-G2 cells. The specificity of 125I IGF-I binding to its receptor was demonstrated by competition studies with monoclonal antibodies directed toward the IGF-I and the insulin receptors, with unlabeled IGF-I and insulin and by affinity labeling experiments. Thus, if IGF-I has any short-term metabolic functions in the adult human liver, it is not through interaction with its own receptor. Autocrine regulation by IGF-I of liver growth appears possible since IGF-I binding sites are expressed under pathological and physiological conditions of growth. The mechanism that couples these two phenomena remains to be elucidated.

Low protein and low phosphorus diet in patients with chronic renal failure: influence on glucose tolerance and tissue insulin sensitivity

Ten patients with advanced renal failure (glomerular filtration rate 25 mL/min) were treated with a low phosphorus and low protein diet supplemented with ketoacid analogues. Before starting the diet and four months afterwards, a 50 g oral glucose tolerance test with a three step euglycemic insulin clamp was carried out. A dose-response curve of total body insulin sensitivity was plotted. By the fourth month, glucose tolerance had improved with significantly lower T0, T30, and T60 insulin levels. These results are attributed to the improvement in insulin action as demonstrated by the clamp technique. The dose-response curve had a distinctly higher plateau after dietary treatment, and the tissue sensitivity index to insulin (M/l ratio) was significantly improved. It is suggested that treatment of uremic patients with a low protein diet may reduce levels of a putative insulin inhibitor.

Effect of chronic uremia on fructose 2,6-bisphosphate glycolytic and gluconeogenic enzymes in rat liver

The level of fructose 2,6-bisphosphate and the maximal activities of key gluconeogenic and glycolytic enzymes were determined in the liver of a rat model of chronic uremia and in ad libitum-fed control and pair-fed control animals. Fructose 2,6-bisphosphate was decreased in uremia and its level negatively correlated with the concentration of blood urea nitrogen. The changes in gluconeogenic enzymes in uremic rats were not different from those in the pair-fed controls. However, pyruvate kinase was decreased in uremia when compared to both controls. These studies offer a possible mechanism for the role of the liver in the carbohydrate intolerance of uremia.

Insulin resistance in uremia: in vitro model in the rat liver using human serum to study mechanisms

We have previously demonstrated in a rat model of chronic uremia that the liver is resistant to insulin. To further investigate the mechanism(s) of insulin resistance in uremia, primary cultures of normal rat hepatocytes were incubated with varying dilutions (1/10 to 1/10,000) of sera from undialyzed end stage uremic and normal humans for 20 hours. We then studied insulin action, binding, and postbinding events. Dilutions of uremic sera as low as 1/1,000 rendered the hepatocytes resistant to maximal concentrations of insulin with regard to [14C]acetate incorporation into lipids. The dose response curve for insulin-stimulated [14C]aminoisobutyric acid uptake demonstrated a shift to the right in hepatocytes incubated with uremic sera when compared with those incubated with normal sera. The 125I-insulin binding sites and affinity, 125I-insulin internalization and degradation, insulin receptor structure, autophosphorylation of the insulin receptor, and its tyrosine-specific kinase activity were normal in the hepatocytes rendered resistant to insulin by uremic sera. However, these cells failed to generate the chemical mediator or second messenger of insulin action, as assessed by its ability to stimulate pyruvate dehydrogenase (PDH) in liver mitochondria from normal rats. We concluded that uremic sera renders normal rat hepatocytes resistant to insulin. Insulin resistance is a postinsulin receptor kinase defect possibly due to lack of the generation of the chemical mediator of insulin action. This in vitro cell model may be useful to further define the mechanism(s) and the serum factor(s) responsible for insulin resistance in uremia in the absence of complicating hormonal and substrate changes that occur in vivo.

Characterization and partial purification of a factor from uremic human serum that induces insulin resistance

We have previously shown that the incubation of normal rat adipose tissue with sera from nondialyzed, nondiabetic uremic patients reduces the transport and metabolism of glucose, in the absence and presence of insulin. In this study insulin-stimulated glucose metabolism by normal rat adipocytes was used as a bioassay to identify the resistance activity, assess the effect of chemical modification on it, and the clinical states associated with its production. The resistance activity was trypsin-labile and had an apparent isoelectric point between 6 and 7, but was not retained by either protein A or concanavalin A columns. The insulin resistance activity was decreased by coincubation with the protein synthesis inhibitor, cycloheximide. Purification to greater than 200,000-fold was attained by heating (100 degrees C) uremic serum, subjecting the supernatant to Sephadex G-25 chromatography and subsequent adsorption to DEAE at pH 7.8 and elution at pH 6.5. The partially purified resistance activity was retained within dialysis tubing of 1,000-mol wt cutoff but not within 2,000-mol wt cutoff. Hemodialysis of patients over 1 wk to 18 mo reduced significantly the amount of resistance activity in their sera. The resistance activity, present in most uremic patients, was not found in the sera of individuals with normal renal function but who were either obese, fasted, elderly or had type II diabetes mellitus. Thus, a circulating small molecular weight peptide, unique to uremia, induced insulin resistance by a protein synthesis-dependent mechanism.