Multiple disturbances of free fatty acid metabolism in noninsulin-dependent diabetes. Effect of oral hypoglycemic therapy

Oleic acid-related anti-inflammatory effects in force-stressed PdL fibroblasts are mediated by H3 lysine acetylation associated with altered IL10 expression

The initiation of a spatially and temporally limited inflammation is essential for tissue and bone remodelling by the periodontal ligament (PdL) located between teeth and alveolar bone. Nutritional components may cause alterations in the inflammatory response of PdL fibroblasts to mechanical stress such as those occurring during orthodontic tooth movement (OTM). Recently, we reported an attenuated pro-inflammatory response of human PdL fibroblasts (HPdLFs) to compressive forces when stimulated with oleic acid (OA), a monounsaturated fatty acid particularly prominent in the Mediterranean diet. Fatty acids could serve as alternative source of acetyl-CoA, thereby affecting epigenetic histone marks, such as histone 3 lysine acetylation (H3Kac) in a lipid metabolism-dependent manner. In this study, we aimed to investigate the extent to which OA exerts its anti-inflammatory effect in compressed HPdLFs via changes in H3Kac. Six-hour compressed HPdLFs showed increased H3Kac when cultured with OA. Inhibition of histone deacetylases resulted in a comparable IL10-increase as observed in compressed OA-cultures. In contrast, inhibition of histone acetyltransferases, particularly p300/CBP, in compressed HPdLFs exposed to OA normalized the inflammatory response to control levels. OA-dependent increased association of H3Kac to IL10 promoter regions in compressed HPdLFs further strengthened the assumption that OA exhibits its anti-inflammatory properties via modulation of this epigenetic mark. In conclusion, our study strongly suggests that nutritional components can directly affect PdL cells via changes in their epigenetic code. Since epigenetic inhibitors are already widely used clinically, they may hold promise for novel approaches for personalized orthodontic treatment that incorporates nutritional and metabolism-related changes.

Palmitate-Triggered COX2/PGE2-Related Hyperinflammation in Dual-Stressed PdL Fibroblasts Is Mediated by Repressive H3K27 Trimethylation

The interrelationships between periodontal disease, obesity-related hyperlipidemia and mechanical forces and their modulating effects on the epigenetic profile of periodontal ligament (PdL) cells are assumed to be remarkably complex. The PdL serves as a connective tissue between teeth and alveolar bone and is involved in pathogen defense and the inflammatory responses to mechanical stimuli occurring during tooth movement. Altered inflammatory signaling could promote root resorption and tooth loss. Hyperinflammatory COX2/PGE2 signaling was reported for human PdL fibroblasts (HPdLFs) concomitantly stressed with Porphyromonas gingivalis lipopolysaccharides and compressive force after exposure to palmitic acid (PA). The aim of this study was to investigate the extent to which this was modulated by global and gene-specific changes in histone modifications. The expression of key epigenetic players and global H3Kac and H3K27me3 levels were quantitatively evaluated in dual-stressed HPdLFs exposed to PA, revealing a minor force-related reduction in repressive H3K27me3. UNC1999-induced H3K27me3 inhibition reversed the hyperinflammatory responses of dual-stressed PA cultures characterized by increased COX2 expression, PGE2 secretion and THP1 adhesion. The reduced expression of the gene encoding the anti-inflammatory cytokine IL-10 and the increased presence of H3K27me3 at its promoter-associated sites were reversed by inhibitor treatment. Thus, the data highlight an important epigenetic interplay between the different stimuli to which the PdL is exposed.

Hyperlipidemic Conditions Impact Force-Induced Inflammatory Response of Human Periodontal Ligament Fibroblasts Concomitantly Challenged with P. gingivalis-LPS

In obese patients, enhanced serum levels of free fatty acids (FFA), such as palmitate (PA) or oleate (OA), are associated with an increase in systemic inflammatory markers. Bacterial infection during periodontal disease also promotes local and systemic low-grade inflammation. How both conditions concomitantly impact tooth movement is largely unknown. Thus, the aim of this study was to address the changes in cytokine expression and the secretion of human periodontal ligament fibroblasts (HPdLF) due to hyperlipidemic conditions, when additionally stressed by bacterial and mechanical stimuli. To investigate the impact of obesity-related hyperlipidemic FFA levels on HPdLF, cells were treated with 200 µM PA or OA prior to the application of 2 g/cm² compressive force. To further determine the additive impact of bacterial infection, HPdLF were stimulated with lipopolysaccharides (LPS) obtained from Porphyromonas gingivalis. In mechanically compressed HPdLF, PA enhanced COX2 expression and PGE2 secretion. When mechanically stressed HPdLF were additionally stimulated with LPS, the PGE2 and IL6 secretion, as well as monocyte adhesion, were further increased in PA-treated cultures. Our data emphasize that a hyperlipidemic condition enhances the susceptibility of HPdLF to an excessive inflammatory response to compressive forces, when cells are concomitantly exposed to bacterial components.

Distinguish fatty acids impact survival, differentiation and cellular function of periodontal ligament fibroblasts

Alveolar bone (AB) remodeling is necessary for the adaption to mechanical stimuli occurring during mastication and orthodontic tooth movement (OTM). Thereby, bone degradation and assembly are strongly regulated processes that can be altered in obese patients. Further, increased fatty acids (FA) serum levels affect bone remodeling cells and we, therefore, investigated whether they also influence the function of periodontal ligament fibroblast (PdLF). PdLF are a major cell type regulating the differentiation and function of osteoblasts and osteoclasts localized in the AB. We stimulated human PdLF (HPdLF) in vitro with palmitic (PA) or oleic acid (OA) and analyzed their metabolic activity, growth, survival and expression of osteogenic markers and calcium deposits. Our results emphasize that PA increased cell death of HPdLF, whereas OA induced their osteoblastic differentiation. Moreover, quantitative expression analysis of OPG and RANKL revealed altered levels in mechanically stimulated PA-treated HPdLF. Furthermore, osteoclasts stimulated with culture medium of mechanical stressed FA-treated HPdLF revealed significant changes in cell differentiation upon FA-treatment. For the first time, our results highlight a potential role of specific FA in the function of HPdLF-modulated AB remodeling and help to elucidate the complex interplay of bone metabolism, mechanical stimulation and obesity-induced alterations.

Influence of New Modified Biliopancreatic Diversion on Blood Glucose and Lipids in GK rats

BACKGROUND

This study aimed to investigate the influence of new biliopancreatic diversion (NBPD) and duodenal-jejunal bypass (DJB) surgery on blood glucose, lipids, gastrointestinal hormones, and insulin in Goto-Kakizaki (GK) rats, an animal model for type 2 diabetes, in order to elucidate the mechanisms underlying the therapeutic effect of these types of surgery on this clinical condition.

METHODS

Thirty 30 male GK rats (SPF) aged 12 weeks were randomly assigned into three groups (n = 10 per group): sham group, NBPD group, and DJB group. Body weight, random plasma glucose, fasting plasma glucose (FPG), oral glucose tolerance (OGT), blood lipids, plasma insulin, glucagon like peptide-1 (GLP-1), and gastric inhibitory polypeptide (GIP) were measured before and after surgery.

RESULTS

NBPD surgery improved glucose tolerance, decreased fasting free fatty acids, triglycerides, and cholesterol. It also increased fasting and postprandial GIP, but caused no change in GLP-1. DJB surgery produced results similar to NBPD surgery except for causing a decrease in postprandial GLP-1 and insulin, and a larger increase in fasting GIP.

CONCLUSIONS

Moving the biliopancreatic duct outlet to the mid-jejunum (NBPD surgery) improves glucose tolerance and increases GIP, but does not change GLP-1. Adding duodenal bypass (DJB surgery) increases fasting GIP and decreases postprandial GLP-1.

A new biliopancreatic diversion surgery decreases plasma glucose and lipids in Goto-Kakizaki rats

AIM: To observe the effects of a new biliopancreatic diversion (NBPD) surgery and duodenal-jejunal bypass (DJB) surgery on plasm glucose and lipids in Goto-Kakizaki (GK) rats and investigate the possibility of surgical treatment of diabetes.

METHODS: Thirty rats were randomly and equally divided into a sham operation group, a NBPD group or a DJB group. The NBPD group and the DJB group underwent NBPD and DJB, respectively, and the sham operation group underwent a sham operation. Body weight, random plasma glucose, OGTT and blood lipids were measured before and after surgery.

RESULTS: One week after surgery, random plasma glucose levels decreased from 17.088 mmol/L ± 3.708 mmol/L to 9.200 mmol/L ± 1.000 mmol/L in the NBPD group and from 17.180 mmol/L ± 3.383 mmol/L to 9.620 mmol/L ± 0.794 mmol/L in the DJB group, respectively, and both were significantly lower than those in the sham operation group. Four weeks postoperatively, fasting cholesterol decreased from 3.220 mmol/L ± 0.185 mmol/L to 3.100 mmol/L ± 0.424 mmol/L in the DJB group and from 3.100 mmol/L ± 0.424 mmol/L to 2.550 mmol/L ± 0.691 mmol/L in the NBPD group.

CONCLUSION: DJB and NBPD decrease plasma glucose and lipids in GK rats possibly via mechanisms associated with diversion of biliopancreatic juice that results in incomplete food digestion and absorption and improves lipid metabolism and plasma glucose.

Palmitic acid and DGAT1 deficiency enhance osteoclastogenesis, while oleic acid-induced triglyceride formation prevents it

Both obesity and diabetes mellitus are associated with alterations in lipid metabolism as well as a change in bone homeostasis and osteoclastogenesis. We hypothesized that increased fatty acid levels affect bone health by altering precursor cell differentiation and osteoclast activation. Here we show that palmitic acid (PA, 16:0) enhances receptor activator of NF-κB ligand (RANKL)-stimulated osteoclastogenesis and is sufficient to induce osteoclast differentiation even in the absence of RANKL. TNFα expression is crucial for PA-induced osteoclastogenesis, as shown by increased TNFα mRNA levels in PA-treated cells and abrogation of PA-stimulated osteoclastogenesis by TNFα neutralizing antibodies. In contrast, oleic acid (OA, 18:1) does not enhance osteoclast differentiation, leads to increased intracellular triglyceride accumulation, and inhibits PA-induced osteoclastogenesis. Adenovirus-mediated expression of diacylglycerol acyl transferase 1 (DGAT1), a gene involved in triglyceride synthesis, also inhibits PA-induced osteoclastogenesis, suggesting a protective role of DGAT1 for bone health. Accordingly, Dgat1 knockout mice have larger bone marrow-derived osteoclasts and decreased bone mass indices. In line with these findings, mice on a high-fat PA-enriched diet have a greater reduction in bone mass and structure than mice on a high-fat OA-enriched diet. Thus, we propose that TNFα mediates saturated fatty acid-induced osteoclastogenesis that can be prevented by DGAT activation or supplementation with OA.

Insulin activation of plasma nonesterified fatty acid uptake in metabolic syndrome

OBJECTIVE

Insulin control of fatty acid metabolism has long been deemed dominated by suppression of adipose lipolysis. The goal of the present study was to test the hypothesis that this single role of insulin is insufficient to explain observed fatty acid dynamics.

METHODS AND RESULTS

Fatty acid kinetics were measured during a meal tolerance test and insulin sensitivity assessed by intravenous glucose tolerance test in overweight human subjects (n=15; body mass index, 35.8 ± 7.1 kg/m(2)). Non-steady state tracer kinetic models were formulated and tested using ProcessDB software. Suppression of adipose fatty acid release, by itself, could not account for postprandial nonesterified fatty acid concentration changes, but adipose suppression combined with insulin activation of fatty acid uptake was consistent with the measured data. The observed insulin K(m) for nonesterified fatty acid uptake was inversely correlated with both insulin sensitivity of glucose uptake (intravenous glucose tolerance test insulin sensitivity; r=-0.626; P=0.01) and whole body fat oxidation after the meal (r=-0.538; P=0.05).

CONCLUSIONS

These results support insulin regulation of fatty acid turnover by both release and uptake mechanisms. Activation of fatty acid uptake is consistent with the human data, has mechanistic precedent in cell culture, and highlights a new potential target for therapies aimed at improving the control of fatty acid metabolism in insulin-resistant disease states.

Plasma nonesterified Fatty Acid intolerance and hyperglycemia are associated with intravenous lipid-induced impairment of insulin sensitivity and disposition index

CONTEXT

It is currently unclear why susceptibility to lipid-induced impairment of beta-cell function varies in different populations.

OBJECTIVE

The aim of the study was to determine whether mild hyperglycemia may be associated with nonesterified fatty acid (NEFA) intolerance and increased iv lipid-induced lipotoxic effect on the beta-cell.

DESIGN AND SETTING

The study consisted of an experimental design with control group conducted at an academic clinical research center.

PARTICIPANTS

Twenty-six overweight or obese individuals (12 with normal glucose tolerance, nine with impaired glucose tolerance or type 2 diabetes, and five subjects who previously had impaired glucose tolerance or type 2 diabetes but at the time of study had normal glucose tolerance after biliopancreatic diversion).

INTERVENTIONS

We assessed insulin sensitivity (S(I)) and beta-cell function [insulin disposition index (DI)] after an overnight iv infusion of heparin + Intralipid (HI) vs. normal saline for 16 h using a stepwise, incremental iv glucose infusion followed by a hyperglycemic clamp.

MAIN OUTCOME MEASURES

We measured S(I), DI, HI-induced change in plasma NEFA, and its association with HI-induced change in S(I) and DI.

RESULTS

HI resulted in significant reduction in S(I) and DI across the three groups of participants. HI-induced elevation of plasma NEFA was higher in hyperglycemic vs. normoglycemic groups. Both fasting glucose level and the magnitude of HI-induced NEFA elevation were associated with the reduction in S(I) (P = 0.007 and P = 0.01, respectively) and DI (P = 0.001 and P = 0.007, respectively).

CONCLUSION

Mild hyperglycemia and NEFA intolerance to iv lipid are associated with susceptibility to lipid-induced reduction in S(I) and DI.

Adipose tissue and liver lipid metabolism in obese children: role of the body mass index and the presence of acanthosis nigricans

AIMS

The aims of our study were to determine if insulin resistance is associated with increased plasma levels of non-esterified fatty acids (NEFA), glycerol, 3-hydroxybutyrate and triglycerides in obese children. We also studied whether the presence of acanthosis nigricans (AN) led to further alterations in the above parameters.

METHODS

A total of 101 children were studied on their first visit to the paediatric endocrine clinic. Seventy-four were obese, 30 of them with AN. The remaining 27 were non-obese healthy children (control group). NEFAs, glycerol, triglycerides, 3-hydroxybutyrate, insulin, leptin, adiponectin and glucose were determined in blood samples obtained after overnight fasting. The insulin resistance index (IRI) was calculated following the homeostasis model assessment (HOMA). Data from the three groups were compared using appropriate statistical tests.

RESULTS

No differences in age, sex ratio and pubertal stage were observed among the three groups. The group of children with the highest body mass index (BMI) showed higher plasma levels of insulin and leptin, higher IRI and lower plasma levels of adiponectin. As insulin and IRI increased, NEFA and 3-hydroxybutyrate decreased and triglycerides increased. When obese children were categorized by BMI, the presence of AN further exacerbated these differences.

CONCLUSIONS

In obese children, insulin resistance is associated with plasma lipid alterations suggestive of both decreased adipose tissue lipolysis and hepatic beta-oxidation and increased hepatic synthesis of triglycerides. Such a metabolic condition may facilitate fat storage and hinder weight loss.

Mechanism of insulin-stimulated clearance of plasma nonesterified fatty acids in humans

Insulin increases plasma nonesterified fatty acid (NEFA) clearance in humans, but whether this is independent of change in plasma NEFA appearance is currently unknown. Nine nondiabetic men (age: 28+/-3 yr, body mass index: 27.2+/-1.7 kg/m2) underwent euglycemic clamps to maintain low (LINS) vs. high (HINS) physiological insulin levels for 6 h. An intravenous infusion of heparin+Intralipid (HI) was performed during 4 of the 6 h of the clamps (in the last 4 h at LINS and in the first 4 h at HINS), whereas saline infusion (SAL) was administered in the remaining 2 h to modulate plasma NEFA levels independently of plasma insulin levels. Four experimental conditions were obtained in each individual: LINS with saline (LINS/SAL) and with HI infusion (LINS/HI) and HINS with saline (HINS/SAL) and with HI infusion (HINS/HI). Plasma palmitate appearance during HINS/SAL was lower than during the three other experimental conditions (P<0.05). In contrast, plasma linoleate appearance, as expected, was increased by HI independently of insulin level (P<0.02). Plasma palmitate clearance during HINS/SAL was higher than LINS/SAL and LINS/HI (P<0.008), and this increase was blunted during HINS/HI. We observed a linear decrease in plasma palmitate clearance with increasing plasma NEFA appearance independent of insulin levels. Plasma NEFA levels increased exponentially with increase in plasma NEFA appearance. We conclude that insulin stimulates plasma NEFA clearance by reducing the endogenous appearance rate of NEFA. The relationship between plasma NEFA level and appearance rate is nonlinear.

Substrate source utilisation in long-term diagnosed type 2 diabetes patients at rest, and during exercise and subsequent recovery

AIMS/HYPOTHESIS

Disturbances in substrate source metabolism and, more particularly, in fatty acid metabolism, play an important role in the aetiology and progression of type 2 diabetes. However, data on substrate source utilisation in type 2 diabetes are inconclusive.

METHODS

[U-(13)C]palmitate and [6,6-(2)H(2)]glucose tracers were used to assess plasma NEFA and glucose oxidation rates and to estimate the use of muscle- and/or lipoprotein-derived triacylglycerol and muscle glycogen. Subjects were ten male patients who had a long-term (7 +/- 1 years) diagnosis of type 2 diabetes and were overweight, and ten matched healthy, male control subjects. Muscle biopsy samples were collected before and after exercise to assess muscle fibre type-specific intramyocellular lipid and glycogen content.

RESULTS

At rest and during exercise, the diabetes patients had greater values than the controls for palmitate rate of appearance (Ra) (rest, 2.46 +/- 0.18 and 1.85 +/- 0.20 respectively; exercise, 3.71 +/- 0.36 and 2.84 +/- 0.20 micromol kg(-1) min(-1)) and rate of disappearance (Rd) (rest, 2.45 +/- 0.18 and 1.83 +/- 0.20; exercise, 3.64 +/- 0.35 and 2.80 +/- 0.20 micromol kg(-1) min(-1) respectively). This was accompanied by significantly higher fat oxidation rates at rest and during recovery in the diabetes patients (rest, 0.11 +/- 0.01 in diabetes patients and 0.09 +/- 0.01 in controls; recovery, 0.13 +/- 0.01 and 0.11 +/- 0.01 g/min respectively), despite significantly greater plasma glucose Ra, Rd and circulating plasma glucose concentrations. Furthermore, exercise significantly lowered plasma glucose concentrations in the diabetes patients, as a result of increased blood glucose disposal.

CONCLUSION

This study demonstrates that substrate source utilisation in long-term-diagnosed type 2 diabetes patients, in whom compensatory hyperinsulinaemia is no longer present, shifts towards an increase in whole-body fat oxidation rate and is accompanied by disturbances in fat and carbohydrate handling.

On the suppression of plasma nonesterified fatty acids by insulin during enhanced intravascular lipolysis in humans

During the fasting state, insulin reduces nonesterified fatty acid (NEFA) appearance in the systemic circulation mostly by suppressing intracellular lipolysis in the adipose tissue. In the postprandial state, insulin may also control NEFA appearance through enhanced trapping into the adipose tissue of NEFA derived from intravascular triglyceride lipolysis. To determine the contribution of suppression of intracellular lipolysis in the modulation of plasma NEFA metabolism by insulin during enhanced intravascular triglyceride lipolysis, 10 healthy nonobese subjects underwent pancreatic clamps at fasting vs. high physiological insulin level with intravenous infusion of heparin plus Intralipid. Nicotinic acid was administered orally during the last 2 h of each 4-h clamp to inhibit intracellular lipolysis and assess insulin's effect on plasma NEFA metabolism independently of its effect on intracellular lipolysis. Stable isotope tracers of palmitate, acetate, and glycerol were used to assess plasma NEFA metabolism and total triglyceride lipolysis in each participant. The glycerol appearance rate was similar during fasting vs. high insulin level, but plasma NEFA levels were significantly lowered by insulin. Nicotinic acid significantly blunted the insulin-mediated suppression of plasma palmitate appearance and oxidation rates by approximately 60 and approximately 70%, respectively. In contrast, nicotinic acid did not affect the marked stimulation of palmitate clearance by insulin. Thus most of the insulin-mediated reduction of plasma NEFA appearance and oxidation can be explained by suppression of intracellular lipolysis during enhanced intravascular triglyceride lipolysis in healthy humans. Our results also suggest that insulin may affect plasma NEFA clearance independently of the suppression of intracellular lipolysis.

Thiazolidinediones upregulate impaired fatty acid uptake in skeletal muscle of type 2 diabetic subjects

We examined the regulation of free fatty acid (FFA, palmitate) uptake into skeletal muscle cells of nondiabetic and type 2 diabetic subjects. Palmitate uptake included a protein-mediated component that was inhibited by phloretin. The protein-mediated component of uptake in muscle cells from type 2 diabetic subjects (78 +/- 13 nmol. mg protein-1. min-1) was reduced compared with that in nondiabetic muscle (150 +/- 17, P < 0.01). Acute insulin exposure caused a modest (16 +/- 5%, P < 0.025) but significant increase in protein-mediated uptake in nondiabetic muscle. There was no significant insulin effect in diabetic muscle (+19 +/- 19%, P = not significant). Chronic (4 day) treatment with a series of thiazolidinediones, troglitazone (Tgz), rosiglitazone (Rgz), and pioglitazone (Pio) increased FFA uptake. Only the phloretin-inhibitable component was increased by treatment, which normalized this activity in diabetic muscle cells. Under the same conditions, FFA oxidation was also increased by thiazolidinedione treatment. Increases in FFA uptake and oxidation were associated with upregulation of fatty acid translocase (FAT/CD36) expression. FAT/CD36 protein was increased by Tgz (90 +/- 22% over control), Rgz (146 +/- 42%), and Pio (111 +/- 37%, P < 0.05 for all 3) treatment. Tgz treatment had no effect on fatty acid transporter protein-1 and membrane-associated plasmalemmal fatty acid-binding protein mRNA expression. We conclude that FFA uptake into cultured muscle cells is, in part, protein mediated and acutely insulin responsive. The basal activity of FFA uptake is impaired in type 2 diabetes. In addition, chronic thiazolidinedione treatment increased FFA uptake and oxidation into cultured human skeletal muscle cells in concert with upregulation of FAT/CD36 expression. Increased FFA uptake and oxidation may contribute to lower circulating FFA levels and reduced insulin resistance in skeletal muscle of individuals with type 2 diabetes following thiazolidinedione treatment.

Lipoproteins abnormalities in obese insulin-resistant dogs

Many studies have shown that obesity and low insulin sensitivity are associated with lipoprotein abnormalities, which are risk factors for coronary heart disease. The effects of insulin resistance on lipoprotein metabolism were investigated in hyperenergetic-fed beagle dogs, a new model of insulin resistance. Insulin resistance was assessed by the 3-hour euglycemic-hyperinsulinemic glucose clamp technique. Lipoproteins were separated by fast-protein liquid chromatography (FPLC) and lipid composition of the different lipoproteins was determined by enzymatic methods. Hyperenergetic diet was associated with a 43% +/- 5% increase in dog body weight and a reduction in insulin-mediated glucose uptake (28 +/- 3 to 16 +/- 1 mg. kg(-1). min(-1), P <.05). Low insulin sensitivity associated with obesity was related to an increase in plasma triglyceride (TG) through an increase in very-low-density lipoprotein (VLDL)-TG (0.071 +/- 0.020 v 0.382 +/- 0.242 mmol/L, P <.05) and high-density lipoprotein (HDL)-TG (0.025 +/- 0.012 v 0.242 +/- 0.143 mmol/L, P <.05). Other lipid abnormalities common in insulin resistant humans were also found: lower plasma HDL-cholesterol (4.690 +/- 0.151 v 3.937 +/- 0.141 mmol/L, P <.05) and higher plasma nonesterified fatty acids (NEFA) (0.974 +/- 0.094 v 1.590 +/- 0.127 mmol/L, P <.05) levels. These data show that this model of the insulin-resistant obese dog could be useful in studying insulin resistance-associated dyslipidemia.

Mechanisms for the deterioration in glucose tolerance associated with HIV protease inhibitor regimens

The mechanisms responsible for the deterioration in glucose tolerance associated with protease inhibitor-containing regimens in HIV infection are unclear. Insulin resistance has been implicated as a major factor, but the affected tissues have not been identified. Furthermore, beta-cell function has not been evaluated in detail. The present study was therefore undertaken to assess the effects of protease inhibitor-containing regimens on hepatic, muscle, and adipose tissue insulin sensitivity as well as pancreatic beta-cell function. We evaluated beta-cell function in addition to glucose production, glucose disposal, and free fatty acid (FFA) turnover using the hyperglycemic clamp technique in combination with isotopic measurements in 13 HIV-infected patients before and after 12 weeks of treatment and in 14 normal healthy volunteers. beta-Cell function and insulin sensitivity were also assessed by homeostasis model assessment (HOMA). Treatment increased fasting plasma glucose concentrations in all subjects (P < 0.001). Insulin sensitivity as assessed by HOMA and clamp experiments decreased by approximately 50% (P < 0.003). Postabsorptive glucose production was appropriately suppressed for the prevailing hyperinsulinemia, whereas glucose clearance was reduced (P < 0.001). beta-Cell function decreased by approximately 50% (P = 0.002), as assessed by HOMA, and first-phase insulin release decreased by approximately 25%, as assessed by clamp data (P = 0.002). Plasma FFA turnover and clearance both increased significantly (P < 0.001). No differences at baseline or in responses after treatment were observed between drug naïve patients who were started on a nucleoside reverse transcriptase inhibitor (NRTI) plus a protease inhibitor and patients who had been on long-term NRTI treatment and had a protease inhibitor added. The present study indicates that protease inhibitor-containing regimens impair glucose tolerance in HIV-infected patients by two mechanisms: 1) inducement of peripheral insulin resistance in skeletal muscle and adipose tissue and 2) impairment of the ability of the beta-cell to compensate.

Nocturnal and postprandial free fatty acid kinetics in normal and type 2 diabetic subjects: effects of insulin sensitization therapy

Whether free fatty acid (FFA) rate of appearance (R(a)) is increased in type 2 diabetes is controversial. To characterize nocturnal and postprandial abnormalities in FFA kinetics and to determine the effects of treatment with insulin sensitizers on lipolysis, we measured palmitate R(a) in control subjects (n = 6) and individuals with poorly controlled, sulfonylurea-treated type 2 diabetes (HbA(1c) = 8.7 +/- 0.2%, n = 20), the latter before and at the end of 12 weeks of treatment with troglitazone (600 mg/day, n = 4), metformin ( approximately 2,000 mg/day, n = 8), or placebo (n = 8). Subjects consumed a standard breakfast at 0800 h. Results in control subjects and type 2 diabetic subjects were compared at baseline. Integrated nocturnal FFA R(a) (AUC(1:00-8:00 A.M.)) was approximately 50% higher in type 2 diabetic subjects than in control subjects (29.4 +/- 3.0 vs. 19.4 +/- 3.9 mmol. m(-2). 7 h(-1), respectively, P < 0.05), whereas postprandial palmitate R(a) (AUC(0-240 min)) was almost threefold higher in type 2 diabetic subjects than in control subjects (14.2 +/- 1.7 vs. 5.3 +/- 1.0 mmol. m(-2). 4 h(-1), respectively, P < 0.01). After troglitazone treatment, nocturnal palmitate R(a) did not change, but postprandial palmitate R(a) decreased by approximately 30% (P < 0.05). Palmitate kinetics did not change with metformin or placebo treatment. In summary, nocturnal and postprandial FFA R(a) is increased in type 2 diabetes. Postprandial lipolysis appears to be preferentially improved by thiazolidinediones compared with nocturnal lipolysis.

Metabolic adaptations in skeletal muscle overexpressing GLUT4: effects on muscle and physical activity

To understand the long-term metabolic and functional consequences of increased GLUT4 content, intracellular substrate utilization was investigated in isolated muscles of transgenic mice overexpressing GLUT4 selectively in fast-twitch skeletal muscles. Rates of glycolysis, glycogen synthesis, glucose oxidation, and free fatty acid (FFA) oxidation as well as glycogen content were assessed in isolated EDL (fast-twitch) and soleus (slow-twitch) muscles from female and male MLC-GLUT4 transgenic and control mice. In male MLC-GLUT4 EDL, increased glucose influx predominantly led to increased glycolysis. In contrast, in female MLC-GLUT4 EDL increased glycogen synthesis was observed. In both sexes, GLUT4 overexpression resulted in decreased exogenous FFA oxidation rates. The decreased rate of FFA oxidation in male MLC-GLUT4 EDL was associated with increased lipid content in liver, but not in muscle or at the whole body level. To determine how changes in substrate metabolism and insulin action may influence energy balance in an environment that encouraged physical activity, we measured voluntary training activity, body weight, and food consumption of MLC-GLUT4 and control mice in cages equipped with training wheels. We observed a small decrease in body weight of MLC-GLUT4 mice that was paradoxically accompanied by a 45% increase in food consumption. The results were explained by a marked fourfold increase in voluntary wheel exercise. The changes in substrate metabolism and physical activity in MLC-GLUT4 mice were not associated with dramatic changes in skeletal muscle morphology. Collectively, results of this study demonstrate the feasibility of altering muscle substrate utilization by overexpression of GLUT4. The results also suggest that as a potential treatment for type II diabetes mellitus, increased skeletal muscle GLUT4 expression may provide benefits in addition to improvement of insulin action.

Insulin resistance and associated metabolic abnormalities in muscle: effects of exercise

Skeletal muscle is a major site of insulin resistance. In addition to glucose transport, oxidative disposal and storage defects, insulin resistant muscle exhibit many other metabolic abnormalities. After a brief review of insulin resistance determinants, we will focus on muscular abnormalities in obesity and type 2 diabetes. Glucose and lipid metabolism defects will be analysed and their interactions discussed. Exercise can improve many of these muscular abnormalities and the mechanisms underlying exercise-induced benefits have been clarified during the past decades. Therefore, exercise training has proved to be useful in the management of insulin resistant states, i.e. mainly obesity, especially in its truncal distribution, and type 2 diabetes. However, exercise prescription remains poorly codified, and results on glycaemic control are sometimes conflicting. In the last part of this review, we will emphasize the pathophysiological basis for an individualized exercise prescription in insulin resistant subjects.

Lack of skeletal muscle uncoupling protein 2 and 3 mRNA induction during fasting in type-2 diabetic subjects

Skeletal muscle uncoupling protein 2 and 3 (UCP-2 and UCP-3) mRNA levels are increased during calorie restriction in lean and nondiabetic obese subjects. In this work, we have investigated the effect of a 5-day hypocaloric diet (1,045 kJ/day) on UCP-2 and UCP-3 gene expression in the skeletal muscle of type-2 diabetic obese patients. Before the diet, UCP-2 and UCP-3 mRNA levels were more abundant in diabetic than in nondiabetic subjects. The long (UCP-3(L)) and short (UCP-3(S)) forms of UCP-3 transcripts were expressed at similar levels in nondiabetic subjects, but UCP-3(S) transcripts were twofold more abundant than UCP-3(L) transcripts in the muscle of diabetic patients. Calorie restriction induced a two- to threefold increase in UCP-2 and UCP-3 mRNA levels in nondiabetic patients. No change was observed in type-2 diabetic patients. Variations in plasma nonesterified fatty acid level were positively correlated with changes in skeletal muscle UCP-3(L) (r = 0.6, P < 0.05) and adipose tissue hormone-sensitive lipase (r = 0.9, P < 0.001) mRNA levels. Lack of increase in plasma nonesterified fatty acid level and in hormone-sensitive lipase upregulation in diabetic patients during the diet strengthens the hypothesis that fatty acids are associated with the upregulation of uncoupling proteins during calorie restriction.

Antidiabetic and hypolipidemic effects of Momordica cymbalaria Hook. fruit powder in alloxan-diabetic rats

This study was undertaken to investigate the effect of Momordica cymbalaria fruit powder on blood glucose and other biochemical parameters in alloxan-induced diabetic rats. The treatment was given for 15 days. After the treatment, a significant reduction was observed in fasting blood glucose levels in the treated diabetic rats, but no hypoglycaemic activity in the treated normal rats. M. cymbalaria treatment showed considerable lowering of serum cholesterol and triglycerides in the treated diabetic group. There was a significant improvement in hepatic glycogen level in treated diabetic rats close to normal level after the treatment with M. cymbalaria. These results suggest that the M. cymbalaria fruit powder possesses antidiabetic and hypolipidemic effects in alloxan-induced diabetic rats.

Abnormal renal and hepatic glucose metabolism in type 2 diabetes mellitus

Release of glucose by liver and kidney are both increased in diabetic animals. Although the overall release of glucose into the circulation is increased in humans with diabetes, excessive release of glucose by either their liver or kidney has not as yet been demonstrated. The present experiments were therefore undertaken to assess the relative contributions of hepatic and renal glucose release to the excessive glucose release found in type 2 diabetes. Using a combination of isotopic and balance techniques to determine total systemic glucose release and renal glucose release in postabsorptive type 2 diabetic subjects and age-weight-matched nondiabetic volunteers, their hepatic glucose release was then calculated as the difference between total systemic glucose release and renal glucose release. Renal glucose release was increased nearly 300% in diabetic subjects (321+/-36 vs. 125+/-15 micromol/min, P < 0.001). Hepatic glucose release was increased approximately 30% (P = 0.03), but increments in hepatic and renal glucose release were comparable (2.60+/-0.70 vs. 2.21+/-0.32, micromol.kg-1.min-1, respectively, P = 0.26). Renal glucose uptake was markedly increased in diabetic subjects (353+/-48 vs. 103+/-10 micromol/min, P < 0.001), resulting in net renal glucose uptake in the diabetic subjects (92+/-50 micromol/ min) versus a net output in the nondiabetic subjects (21+/-14 micromol/min, P = 0.043). Renal glucose uptake was inversely correlated with renal FFA uptake (r = -0.51, P < 0.01), which was reduced by approximately 60% in diabetic subjects (10. 9+/-2.7 vs. 27.0+/-3.3 micromol/min, P < 0.002). We conclude that in type 2 diabetes, both liver and kidney contribute to glucose overproduction and that renal glucose uptake is markedly increased. The latter may suppress renal FFA uptake via a glucose-fatty acid cycle and explain the accumulation of glycogen commonly found in the diabetic kidney.

Human kidney free fatty acid and glucose uptake: evidence for a renal glucose-fatty acid cycle

To determine the relationship between free fatty acids (FFA) and glucose uptake by the human kidney, 12 postabsorptive normal volunteers underwent renal vein catheterization and were infused to isotopic steady state with [6-3H]glucose and [9,10-3H]palmitate. Arterial and renal vein palmitate specific activities were not significantly different (3,533 +/- 219 vs. 3,549 +/- 220 dpm/mumol, P = 0.64). Palmitate renal fractional extraction and uptake determined isotopically (7.2 +/- 1.1% and 9.1 +/- 1.4 mumol/min) were not significantly different from those calculated by net balance measurements (8.3 +/- 1.2% and 9.7 +/- 1.2 mumol/min, P > 0.07 and P > 0.7, respectively). Renal palmitate uptake accounted for 8.7 +/- 1.3% of its systemic turnover. Renal linoleate and oleate fractional extraction calculated by net balance measurements (8.0 +/- 0.9 and 7.7 +/- 1.2%, respectively) were not significantly different from each other and that of palmitate (all P > 0.7). Renal uptake of palmitate, linoleate (7.9 +/- 1.0 mumol/min), and oleate (10.9 +/- 2.0 mumol/min) were all directly proportional to their arterial concentrations (r = 0.70, 0.68, and 0.63, respectively, all P < 0.025). Renal glucose uptake (93 +/- 10 mumol/min) accounted for 12.6 +/- 1.5% of its systemic turnover and was inversely related to the sum of palmitate, linoleate, and oleate uptake (r = -0.74, P < 0.01). These data indicate that in postabsorptive humans: 1) the kidney is an important site of FFA and glucose disposal, 2) a renal glucose-fatty acid cycle may exist, and 3) there appears to be little or no release into the circulation of stored renal FFA.

Causal linkage between insulin suppression of lipolysis and suppression of liver glucose output in dogs

Suppression of hepatic glucose output (HGO) has been shown to be primarily mediated by peripheral rather than portal insulin concentrations; however, the mechanism by which peripheral insulin suppresses HGO has not yet been determined. Previous findings by our group indicated a strong correlation between free fatty acids (FFA) and HGO, suggesting that insulin suppression of HGO is mediated via suppression of lipolysis. To directly test the hypothesis that insulin suppression of HGO is causally linked to the suppression of adipose tissue lipolysis, we performed euglycemic-hyperinsulinemic glucose clamps in conscious dogs (n = 8) in which FFA were either allowed to fall or were prevented from falling with Liposyn plus heparin infusion (LI; 0.5 ml/min 20% Liposyn plus 25 U/min heparin with a 250 U prime). Endogenous insulin and glucagon were suppressed with somatostatin (1 microgram/min/kg), and insulin was infused at a rate of either 0.125 or 0.5 mU/min/kg. Two additional experiments were performed at the 0.5 mU/min/kg insulin dose: a double Liposyn infusion (2 x LI; 1.0 ml/min 20% Liposyn, heparin as above), and a glycerol infusion (19 mg/min). With the 0.125 mU/min/kg insulin infusion, FFA fell 40% and HGO fell 33%; preventing the fall in FFA with LI entirely prevented this decline in HGO. With 0.5 mU/min/kg insulin infusion, FFA levels fell 64% while HGO declined 62%. Preventing the fall in FFA at this higher insulin dose largely prevented the fall in HGO; however, steady state HGO still declined by 18%. Doubling the LI infusion did not further affect HGO, suggesting that the effect of FFA on HGO is saturable. Elevating plasma glycerol levels did not alter insulin's ability to suppress HGO. These data directly support the concept that insulin suppression of HGO is not direct, but rather is mediated via insulin suppression of adipose tissue lipolysis. Thus, resistance to insulin control of hepatic glucose production in obesity and/or non-insulin-dependent diabetes mellitus may reflect resistance of the adipocyte to insulin suppression of lipolysis.

Metabolic response of forearm muscle to graded exercise in type II diabetes mellitus: effect of endurance training

In this study, 31P nuclear magnetic resonance spectroscopy was used to monitor muscle metabolism in Type II diabetic subjects (n = 10) during an incremental exercise test. Also the exercise responses of diabetic subjects (n = 4) following submaximal endurance training were assessed and compared to healthy controls (n = 5). Responses to incremental exercise in the diabetic subjects were consistent over time despite minor fluctuations in metabolic control. In the diabetic and control groups, after 12 weeks of training the forearm flexor muscles, power output at the intracellular threshold of acidosis (IT) increased (p < .01) similarly: T0 versus T12: 0.90 +/- 0.09 versus 1.20 +/- 0.13 and 1.03 +/- 0.07 versus 1.22 +/- 0.10 W, respectively. Minimum intracellular pH reached at peak exercise was unchanged after training. The control group, however, became more acidic versus the diabetic group (p < .05) in response to progressive exercise. This difference was maintained over time. Endurance training elicited similar adaptations in forearm muscles of Type II diabetic and control subjects, although there were differences between the two groups in intracellular pH during exercise.

Effects of Acipimox on the metabolism of free fatty acids and very low lipoprotein triglyceride

The mechanism of triglyceride lowering by Acipimox, a nicotine acid analogue, was examined in a group of five moderately hypertriglyceridemic male rhesus monkeys. Two experiments were designed to examine the effect of the drug on lipid and glucose metabolism in nondiabetic, insulin-resistant animals. A single dose of Acipimox (8 mg/kg) given with a meal lowered the plasma free fatty acids (FFA) significantly at 4 h (0.102 +/- 0.008 vs 0.154 +/- 0.020 g/l; mean +/- SEM; P < 0.03); however, FFA concentrations returned to control levels at 6 h. Chronic administration of Acipimox (16 mg/kg q. i. d.) for 2 months produced a 31% reduction in triglyceride concentration (P < 0.05) and a significant decrease in low density lipoprotein (LDL)-cholesterol (P < 0.04), without changes in insulin action as measured by the hyperinsulinemic euglycemic clamp. Fasting FFA concentrations were not significantly altered by chronic treatment (0.163 +/- 0.013 versus 0.140 +/- 0.034 g/l). Fatty acid metabolic studies indicated increases in FFA transport (203.7 +/- 59.1 versus 136.1 +/- 26.6 microEq/min; P < 0.05), while FFA fractional clearance rate (FCR) was unchanged. Very low density lipoprotein triglyceride (VLDL-Tg) metabolic experiments, using [3H]glycerol, showed increases in production and FCR with the drug. Increased VLDL-Tg clearance, in spite of increased production of VLDL, appears to be the mechanism by which triglycerides are lowered upon chronic Acipimox administration.

Impaired free fatty acid utilization by skeletal muscle in non-insulin-dependent diabetes mellitus

This study was undertaken to assess utilization of FFA by skeletal muscle in patients with non-insulin-dependent diabetes mellitus (NIDDM). 11 NIDDM and 9 nondiabetic subjects were studied using leg balance methods to measure the fractional extraction of [3H]oleate. Limb indirect calorimetry was used to estimate RQ. Percutaneous muscle biopsy samples of vastus lateralis were analyzed for muscle fiber type distribution, capillary density, and metabolic potential as reflected by measurements of the activity of seven muscle enzyme markers of glycolytic and aerobic-oxidative pathways. During postabsorptive conditions, fractional extraction of oleate across the leg was lower in NIDDM subjects (0.31 +/- 0.08 vs. 0.43 +/- 0.10, P < 0.01), and there was reduced oleate uptake across the leg (66 +/- 8 vs. 82 +/- 13 nmol/min, P < 0.01). Postabsorptive leg RQ was increased in NIDDM (0.85 +/- 0.03 vs. 0.77 +/- 0.02, P < 0.01), and rates of lipid oxidation by skeletal muscle were lower while glucose oxidation was increased (P < 0.05). In subjects with NIDDM, proportions of type I, IIa, and IIb fibers were 37 +/- 2, 37 +/- 6, and 26 +/- 5%, respectively, which did not differ from nondiabetics; and capillary density, glycolytic, and aerobic-oxidative potentials were similar. During 6 h after ingestion of a mixed meal, arterial FFA remained greater in NIDDM subjects. Therefore, despite persistent reduced fractional extraction of oleate across the leg in NIDDM (0.34 +/- 0.04 vs. 0.38 +/- 0.03, P < 0.05), rates of oleate uptake across the leg were greater in NIDDM (54 +/- 7 vs. 45 +/- 8 nmol/min, P < 0.01). In summary, during postabsorptive conditions there is reduced utilization of FFA by muscle, while during postprandial conditions there is impaired suppression of FFA uptake across the leg in NIDDM. During both fasting and postprandial conditions, NIDDM subjects have reduced rates of lipid oxidation by muscle.

Associations between insulin sensitivity, and free fatty acid and triglyceride metabolism independent of uncomplicated obesity

Insulin resistance is associated with hypertriglyceridemia and elevated free fatty acid (FFA) concentrations in obese and diabetic individuals, but it is unclear to what extent this relationship is independent of obesity and is present in healthy individuals. We studied 92 healthy middle-aged males selected from the top, middle, and lowest quintiles of the insulin sensitivity index (Si) determined in a group of 182 men using the minimal model of glucose disappearance. Plasma FFA, triglyceride, glucose, insulin, and C-peptide concentrations were measured during a 3-hour intravenous glucose tolerance test (IVGTT). The low-Si (most insulin-resistant) group had more central body fat distribution (subscapular/triceps skinfold thickness) and a higher median body mass index (BMI) of 26.8 (range, 21.1 to 41.1) kg.m-2 compared with the middle- and high-Si groups with BMIs of 24.9 (19.1 to 31.5) and 23.7 (18.8 to 33.2) kg.m-2 (P < .05). Relatively minor glucose intolerance in the low-Si group was no longer significant when central adiposity was accounted for. Glucose tolerance was maintained by increased insulin secretion, leading to IVGTT insulin responses twofold and fourfold higher in the middle- and low-Si groups, respectively, compared with the high-Si group (P < .01). Fasting FFA and triglyceride concentrations were increased in the low-Si group relative to the other groups independent of BMI or central adiposity (P < .01). During the IVGTT, FFA decreased to similar minimum concentrations in all three groups. Triglyceride concentrations during the IVGTT increased above their minimum levels, particularly in the low-Si group (P < .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Glucose metabolism in incubated human muscle: effect of obesity and non-insulin-dependent diabetes mellitus

Skeletal muscle contributes significantly to reduced insulin-stimulated glucose disposal in patients with obesity and non-insulin-dependent (type II) diabetes mellitus (NIDDM). The biochemical basis for insulin resistance is not known but may involve reduced glucose transport and/or a defect in intracellular pathways for glucose disposal. To address this question, we measured basal and insulin-stimulated glucose oxidation, glycogen formation, and nonoxidative glycolysis (lactate and amino acid release) in an incubated muscle preparation from nonobese and morbidly obese patients with and without NIDDM. Pathways of glucose disposal were also determined in muscle of obese NIDDM patients incubated under hyperglycemic (20 mmol/L) conditions, which increases glucose uptake by mass action. Under basal conditions (no insulin present) there were no significant differences in glycogen formation or glucose oxidation between nonobese control, obese nondiabetic, or obese diabetics. Lactate release was significantly higher in obese controls compared to nonobese controls in the basal state at 5 mmol/L glucose (10.2 +/- 2.8 v 24.7 +/- 3.5 nmol/min/g, P < .05). Under maximal insulin-stimulated conditions, rates of glycogen formation, glucose oxidation, and nonoxidized glycolysis increased 1.9-, 2.3-, and 2.2-fold over basal (P < .05) in nonobese controls. By contrast, insulin was ineffective at stimulating significant increases in any metabolic pathway of glucose disposal in muscle of obese or obese NIDDM patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Fast gas chromatographic-mass spectrometric method for the evaluation of plasma fatty acid turnover using [1-13C]palmitate

Turnover of plasma free fatty acids (FFAs) can be determined from the palmitate enrichment of plasma after administration of analogues labeled with stable isotopes. We studied the conditions to measure both the concentration and the 13C enrichment of plasma palmitate by gas chromatography-mass spectrometry (GC-MS) using crude extracts. The method used plasma extraction after addition of heptadecanoic acid as internal standard and methylation with diazomethane. Subsequently the samples were analyzed by GC-MS. Plasma palmitate levels determined with this simplified method did not differ statistically from those obtained by a more "classical" procedure using FFA separation from other plasma lipids. Palmitic acid turnover rates (Ra) were evaluated in the steady-state period, in two normal subjects after 90 min infusion with [1-13C]palmitate bound to human albumin. The rate of appearance (Ra) was found to be 0.92 and 1.08 mmol kg-1 min-1, which is in good agreement with the turnover rate previously reported for normal subjects. Sample preparation and GC-MS analysis by the proposed procedure are simple and rapid and thus the method appears to be particularly useful in clinical studies where numerous samples have to be analyzed.

The effect of an antilipolytic agent (acipimox) on the insulin resistance of lipid and glucose metabolism in hypertriglyceridaemic patients

Hypertriglyceridaemia is associated with insulin resistance of both lipid and glucose metabolism. It is not known whether the insulin resistance affects both glucose oxidation and glycogen formation. To study the oxidative and non-oxidative pathways of non-esterified fatty acids (NEFA) and glucose metabolism, eight male hypertriglyceridaemic subjects were studied during insulin infusion (75 and 340 pmol/m2.min) in combination with indirect calorimetry and infusions of [3-3H]glucose and [1-14C]palmitate before and after 4 weeks of treatment with the antilipolytic agent acipimox (250 mg three times daily). Compared with eight healthy subjects the hypertriglyceridaemic subjects were resistant to the antilipolytic effect of insulin, both in the basal state (P < 0.05) and during insulin infusion (P < 0.05). This was associated with impaired insulin-stimulated glucose uptake (P < 0.05), predominantly in the non-oxidative pathway (P < 0.05). Acipimox decreased basal NEFA concentrations (P < 0.01) and reduced lipid oxidation during low-dose insulin infusion (P < 0.05). Glucose uptake, predominantly glycogen formation, was stimulated by acipimox (P < 0.05). In conclusion, the insulin resistance of glucose metabolism associated with hypertriglyceridaemia is largely due to a defect in non-oxidative glucose metabolism. Acipimox improves glucose metabolism both by affecting glucose oxidation (low-dose insulin) and non-oxidative glucose metabolism (high-dose insulin).

Different acute and chronic effects of acipimox treatment on glucose and lipid metabolism in patients with type 2 diabetes

To study whether therapeutic reduction of non-esterified fatty acids (NEFA) can be used to improve glucose metabolism, we administered the antilipolytic agent, acipimox, 250 mg four times daily for 4 weeks in eight obese Type 2 diabetic patients. Glucose and NEFA metabolism were assessed before and after treatment with a two-step euglycaemic hyperinsulinaemic clamp (0.25 and 1 mU kg-1 min-1 insulin) combined with infusions of [3-3H] glucose and [1-14C] palmitate. Three days of acipimox treatment reduced 24-h serum NEFA levels by 10%, but the difference disappeared after 4 weeks of treatment mainly due to a two-fold rise in morning NEFA concentrations (p < 0.01). After 3 days of acipimox treatment, fasting and 24-h plasma glucose and serum triglyceride concentrations were significantly reduced (p < 0.05), but no longer after 4 weeks of treatment. Despite the rebound rise in NEFA, acute administration of acipimox still inhibited both oxidative and non-oxidative NEFA metabolism in the basal state (p < 0.01-0.001) and during insulin infusion (p < 0.05-0.001). Inhibition of NEFA metabolism was associated with increased insulin-stimulated glucose uptake (from 3.56 +/- 0.28 to 5.14 +/- 0.67 mumol kg-1 min-1, p < 0.05), mainly due to stimulation of non-oxidative glucose disposal (from 1.74 +/- 0.23 to 3.03 +/- 0.53 mumol kg-1 min-1, p < 0.05). In conclusion, acipimox administered acutely inhibits NEFA appearance (lipolysis), which is associated with improved glucose uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin action and substrate competition

An increased supply of FFAs for oxidation leads to a reduced rate of glucose oxidation and interferes with the inhibitory action of insulin on hepatic glucose production. Available evidence indicates that in humans skeletal muscle is a site for such substrate competition, which involves both pyruvate oxidation and glycogen synthesis. The insulin resistance of obesity is thought to be mostly of metabolic origin, and fully reversible. A reduction in FFA supply by weight reduction can, however, reverse this defect. The insulin resistance associated with NIDDM is thought to be primary, with a strong genetic basis, and partially irreversible. Patients with NIDDM are unable to increase their glucose oxidation normally in response to insulin to meet the energy demands of the body. Increased oxidation of lipids represents a compensatory phenomenon to meet these demands. Therapeutic use of the glucose-FFA cycle to lower blood glucose levels has yielded conflicting results. Studies are in progress to develop agents that inhibit gluconeogenesis by interfering with FFA oxidation. Nicotinic acid derivatives seem to enhance glycogen synthesis acutely by activating glycogen synthetase. Whether these or similar agents can be used to restore impaired glycogen synthesis, the most characteristic genetic defect in NIDDM, cannot be answered until the effect has been proven in chronic studies. The existence of substrate competition between amino acids and glucose, and an intrinsic hypoaminoacidaemic property of amino acids, makes it possible to expand the Randel cycle into a glucose-FFA-amino acid cycle, which integrates control of substrate disposition at the whole body level.

Peripheral and hepatic insulin sensitivity in non-insulin-dependent diabetes mellitus: effect of nonesterified fatty acids

Plasma nonesterified fatty acid (NEFA) levels are increased in the insulin-stimulated state in non-insulin-dependent diabetes mellitus (NIDDM) and may contribute to the decrease in peripheral and hepatic insulin sensitivity. To test this hypothesis and to avoid the confounding effect of obesity, we examined the effect of decreasing plasma NEFA levels on peripheral and total glucose metabolism in eight non-obese, NIDDM patients. Each received 250 mg Acipimox (a nicotinic acid analogue) or placebo at 0 and 120 minutes on separate occasions. [6,6-2H2]-glucose (0 to 300 minutes) and insulin (120 to 300 minutes) were infused in each study, and isoglycemia was maintained. Plasma NEFA levels (140 +/- 30 v 600 +/- 70 mumol/L [SEM]; P < .001) and forearm NEFA uptake measured with [1-14C]-palmitate (+93 +/- 21 v +313 +/- 42 nmol x 100 mL forearm-1; P < .001) were decreased with acipimox during the basal period (90 to 120 minutes), with no change in forearm glucose uptake (+334 +/- 80 and +330 +/- 60 nmol x 100 mL forearm-1 x min-1) and hepatic glucose output ([HGO] 13.6 +/- 0.9 and 13.4 +/- 0.7 mumol.kg-1 x min-1). Serum insulin (256 +/- 12 and 266 +/- 18 pmol/L) and plasma glucose (9.5 +/- 0.6 and 9.4 +/- 0.5 mmol/L) levels were comparable during the clamp period (270 to 300 minutes).(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin resistance in the regulation of lipolysis and ketone body metabolism in non-insulin dependent diabetes is apparent at very low insulin concentrations

The insulin sensitivity of intermediary metabolism was studied in 8 non-obese men with well-controlled diet-treated non-insulin dependent diabetes (NIDDM) using a low dose incremental insulin infusion (basal, 0.005 and 0.01 U/kg h-1). Results were compared to 8 healthy male control subjects matched (NIDDM vs. controls, mean +/- S.E.M.) for age (56 +/- 3 vs. 54 +/- 3 years, NS) and body mass index (24.6 +/- 0.7 vs. 25.3 +/- 0.5 kg/m2, NS). Basal fasting concentrations of insulin (4.7 +/- 0.8 vs. 3.2 +/- 0.8 mU/l, NS), glucose, total ketone bodies (TKB), and non-esterified fatty acids (NEFA) were not significantly different between the groups but glycerol concentrations were significantly elevated in NIDDM patients (0.072 +/- 0.007 vs. 0.049 +/- 0.003 mmol/l, P < 0.05). During incremental insulin infusion, plasma insulin concentrations rose to 12.8 +/- 1.5 vs. 10.0 +/- 1.0 mU/l in NIDDM patients vs. control and metabolite concentrations fell significantly (P < 0.001). Significant linear dose-response relationships were found between plasma insulin (log) and glucose, TKB (log), NEFA, and glycerol concentrations by analysis of variance applied to regression (all P < 0.001). For glucose and TKB (log), the group regression lines were parallel but were significantly right-shifted in the NIDDM group (P < 0.001). In contrast, the relationships of insulin (log) and both glycerol and NEFA concentrations converged over the observed range of insulin concentrations. Significant displacement of glycerol and NEFA dose-response relationships were found in NIDDM patients at an insulin concentration of 5 mU/l (P < 0.001) but not at 12.5 mU/l.(ABSTRACT TRUNCATED AT 250 WORDS)

Lowering of triglycerides by gemfibrozil affects neither the glucoregulatory nor antilipolytic effect of insulin in type 2 (non-insulin-dependent) diabetic patients

Hypertriglyceridaemia and insulin resistance are closely associated but it is unknown whether hypertriglyceridaemia per se contributes to insulin resistance. In the present study we examined whether gemfibrozil, by lowering triglyceride levels, improves the glucoregulatory and antilipolytic action of insulin in Type 2 (non-insulin-dependent) diabetes mellitus. Twenty patients were randomly allocated to receive either placebo or gemfibrozil 1200 mg daily for 12 weeks in a double-blind study. Very low density lipoprotein triglyceride levels decreased in the gemfibrozil group by 42 +/- 12% (p < 0.01). Gemfibrozil had no effect on the diurnal concentration of non-esterified fatty acids (NEFA). At the randomization HbA1c levels were comparable (7.6 +/- 0.3 vs 7.8 +/- 0.2%, NS) and increased slightly both in the gemfibrozil (8.2 +/- 0.4%, p < 0.05) and placebo groups (8.0 +/- 0.3%, NS). Pre- and post-treatment diurnal glucose and insulin concentrations remained unchanged. Basal pre- and post-treatment hepatic glucose production rates were comparable in both groups and similarly suppressed by insulin. Rate of whole body glucose disposal during a low-dose insulin infusion (serum insulin -90 pmol/l) (pre- vs post-gemfibrozil 11.9 +/- 1.1 vs 11.1 +/- 0.7, pre- vs post-placebo 9.9 +/- 1.1 vs 10.8 +/- 0.8 mumol.kg-1.min-1, NS for both) and a high-dose insulin infusion (serum insulin approximately 500 pmol/l) (16.2 +/- 1.7 vs 17.7 +/- 2.7, 17.1 +/- 4.2 vs 17.4 +/- 2.9 mumol.kg-1 x min-1, respectively, NS for both) remained unchanged. Basal pre- and post-treatment NEFA turnover rates were comparable in both groups and similarly suppressed by insulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of free fatty acid metabolism by insulin in humans: role of lipolysis and reesterification

The regulation of lipolysis, free fatty acid appearance into plasma (FFA R(a)), an FFA reesterification and oxidation were examined in seven healthy humans infused intravenously with insulin at rates of 4, 8, 25, and 400 mU.m-2.min-1. Glycerol and FFA R(a) were determined by isotope dilution methods, and FFA oxidation was calculated by indirect calorimetry or by measurement of expired 14CO2 from infused [1-14C]palmitate. These measurements were used to calculate total FFA reesterification, primary FFA reesterification occurring within the adipocyte, and secondary reesterification of circulating FFA molecules. Lipolysis, FFA R(a), and secondary FFA reesterification were exquisitely insulin sensitive [the insulin concentrations that produced half-maximal suppression (EC50), 106 +/- 26, 91 +/- 20 vs. 80 +/- 16 pM, P = not significant] in contrast to insulin suppression of FFA oxidation (EC50, 324 +/- 60, all P < 0.01). The absolute rate of primary FFA reesterification was not affected by the increase in insulin concentration, but the proportion of FFA molecules undergoing primary reesterification doubled over the physiological portion of the insulin dose-response curve (from 0.23 +/- 0.06 to 0.44 +/- 0.07, P < 0.05). This served to magnify insulin suppression of FFA R(a) twofold. In conclusion, insulin regulates FFA R(a) by inhibition of lipolysis while maintaining a constant rate of primary FFA reesterification.

Effects of different lipid substrates on glucose metabolism in normal postabsorptive humans

We investigated the effects on glucose metabolism of the infusion of either long-chain triglycerides (LCT), a mixture of long-chain and medium-chain triglycerides (MCT/LCT), D-beta-hydroxybutyrate (D-beta-OHB), or saline in normal postabsorptive subjects. Plasma insulin, C-peptide, and glucagon concentrations were unchanged in all groups. LCT and MCT/LCT infusions increased levels of plasma free fatty acids (FFA) compared with those of the saline group, whereas D-beta-OHB decreased them. Plasma ketone body concentrations were higher during the D-beta-OHB and triglyceride infusions than during the saline test. Glucose concentrations and appearance (Ra) and disappearance (Rd) rates were not modified during saline infusion. Glucose levels decreased only in the D-beta-OHB and MCT/LCT groups (P < .05), whereas they were unchanged during LCT infusion. Glucose Ra decreased slightly by 15% to 17% in LCT, MCT/LCT, and D-beta-OHB groups (P < .05 v saline). Glucose Rd decreased by 14% to 16% in each lipid-infusion group (P < .05 v saline). Glucose clearance rates decreased by 14% only in the LCT group (P < .001). Glucose oxidation rates did not change significantly during the lipid substrate infusions compared with saline infusion. In conclusion, (1) the effects of fatty acids on glucose metabolism appear to depend on the fatty acid chain length, since only LCT infusion significantly impaired glucose utilization; and (2) in subjects with normal endocrine pancreas function, we found no adverse effects of a short-term increase in lipid substrate availability on glucose production rate and concentration.

Adrenergic mechanisms contribute to the late phase of hypoglycemic glucose counterregulation in humans by stimulating lipolysis

Three studies were performed on nine normal volunteers to assess whether catecholamine-mediated lipolysis contributes to counterregulation to hypoglycemia. In these three studies, insulin was intravenously infused for 8 h (0.30 mU.kg-1.min-1 from 0 to 180 min, and 0.40 mU.kg-1.min-1 until 480 min). In study I (control study), only insulin was infused; in study II (direct + indirect effects of catecholamines), propranolol and phentolamine were superimposed to insulin and exogenous glucose was infused to reproduce the same plasma glucose (PG) concentration of study I. Study III (indirect effect of catecholamines) was the same as study II, except heparin (0.2 U.kg-1.min-1 after 80 min), 10% Intralipid (1 ml.min-1 after 160 min) and variable glucose to match PG of study II, were also infused. Glucose production (HGO), glucose utilization (Rd) [3-3H]glucose, and glucose oxidation and lipid oxidation (LO) (indirect calorimetry) were determined. In all three studies, PG decreased from approximately 4.8 to approximately 2.9 mmol/liter (P = NS between studies), and plasma glycerol and FFA decreased to a nadir at 120 min. Afterwards, in study I plasma glycerol and FFA increased by approximately 75% at 480 min, but in study II they remained approximately 40% lower than in study I, whereas in study III they rebounded as in study I (P = NS). In study II, LO was lower than in study I (1.69 +/- 0.13 vs. 3.53 +/- 0.19 mumol.kg-1.min-1, P less than 0.05); HGO was also lower between 60 and 480 min (7.48 +/- 0.57 vs. 11.6 +/- 0.35 mumol.kg-1.min-1, P less than 0.05), whereas Rd was greater between 210 and 480 min (19 +/- 0.38 vs. 11.4 +/- 0.34 mumol.kg-1.min-1, respectively, P less than 0.05). In study III, LO increased to the values of study I; between 4 and 8 h, HGO increased by approximately 2.5 mumol.kg-1.min-1, and Rd decreased by approximately 7 mumol.kg-1.min-1 vs. study II. We conclude that, in a late phase of hypoglycemia, the indirect effects of catecholamines (lipolysis mediated) account for at least approximately 50% of the adrenergic contribution to increased HGO, and approximately 85% of suppressed Rd.

Studies on the mechanism of action of sulphonylureas in type II diabetic subjects: gliquidone

The mechanism of action of sulphonylureas is not completely understood. In the present study we evaluated the effects of gliquidone, a second-generation compound, on several metabolic parameters in 22 patients with untreated newly-diagnosed type II (noninsulin-dependent) diabetes mellitus. After either 1 or 6 months of treatment with gliquidone plus isocaloric diet we observed: 1) a significant decrease in fasting plasma glucose and glycemic profile after oral glucose load; 2) unchanged fasting and postglucose plasma insulin levels; 3) no change in fasting C-peptide levels but a significant increase in C-peptide concentrations after glucose challenge; 4) a significant increase in glucose disappearance rate from plasma following iv insulin injection; 5) an increase in the insulin-induced reduction of plasma levels of free-fatty acids; 6) no change in plasma C-peptide levels following iv insulin injection; 7) a significant increase in specific insulin binding to monocytes. After 6 but not 1 month of gliquidone therapy we also found an increase in the activity of hexokinase in circulating mononuclear leukocytes. These results suggest that the hypoglycemic effect of gliquidone occurs through either an increased beta cell response to glucose stimulus or an enhanced insulin sensitivity. The latter effect seems to depend on both receptor and postreceptor mechanisms.

Increased lipolysis and its consequences on gluconeogenesis in non-insulin-dependent diabetes mellitus

The present studies were undertaken to determine whether lipolysis was increased in non-insulin-dependent diabetes mellitus (NIDDM) and, if so, to assess the influence of increased glycerol availability on its conversion to glucose and its contribution to the increased gluconeogenesis found in this condition. For this purpose, we infused nine subjects with NIDDM and 16 age-, weight-matched nondiabetic volunteers with [2-3H] glucose and [U-14C] glycerol and measured their rates of glucose and glycerol appearance in plasma and their rates of glycerol incorporation into plasma glucose. The rate of glycerol appearance, an index of lipolysis, was increased 1.5-fold in NIDDM subjects (2.85 +/- 0.16 vs. 1.62 +/- 0.08 mumol/kg per min, P less than 0.001). Glycerol incorporation into plasma glucose was increased threefold in NIDDM subjects (1.13 +/- 1.10 vs. 0.36 +/- 0.02 mumol/kg per min, P less than 0.01) and accounted for twice as much of hepatic glucose output (6.0 +/- 0.5 vs. 3.0 +/- 0.2%, P less than 0.001). Moreover, the percent of glycerol turnover used for gluconeogenesis (77 +/- 6 vs. 44 +/- 2, P less than 0.001) was increased in NIDDM subjects and, for a given plasma glycerol concentration, glycerol gluconeogenesis was increased more than two-fold. The only experimental variable significantly correlated with the increased glycerol gluconeogenesis after taking glycerol availability into consideration was the plasma free fatty acid concentration (r = 0.80, P less than 0.01). We, therefore, conclude that lipolysis is increased in NIDDM and, although more glycerol is thus available, increased activity of the intrahepatic pathway for conversion of glycerol into glucose, due at least in part to increased plasma free fatty acids, is the predominant mechanism responsible for enhanced glycerol gluconeogenesis. Finally, although gluconeogenesis from glycerol in NIDDM is comparable to that of alanine and about one-fourth that of lactate is terms of overall flux into glucose, glycerol is probably the most important gluconeogenic precursor in NIDDM in terms of adding new carbons to the glucose pool.

Hepatic sensitivity to insulin: effects of sulfonylurea drugs

Insulin regulation of hepatic glucose production (HGP) is altered in non-insulin-dependent diabetes mellitus (NIDDM), resulting in increased glucose output by the liver; this contributes to the elevation in plasma glucose concentration observed both in the basal state and postprandially. Therefore, restoration of normal insulin action in the liver must be a goal of hypoglycemic therapy. Sulfonylureas have been widely used for treatment of NIDDM over the past 30 years. In addition to their stimulatory effect on insulin secretion, these compounds seem to possess extrapancreatic effects. Early in vitro studies showed that addition of sulfonylureas to the perfusion medium of liver preparations could exert a significant suppressive effect on HGP. Subsequent experience suggested that these compounds could act at the level of the insulin receptor as well as at various postreceptor sites. These studies showed that sulfonylureas may inhibit glycogenolysis and gluconeogenesis while stimulating glycogen synthesis. Results obtained in vivo in NIDDM patients are in agreement with the in vitro studies. Long-term treatment with sulfonylureas is associated with a decline in fasting plasma glucose concentration and a parallel reduction in HGP. Nevertheless, the direct effect of sulfonylurea administration on the liver remains unclear, since the reduction in HGP that occurs during sulfonylurea treatment may be secondary to an overall improvement in insulin secretion. It is also of interest that in insulin-dependent diabetic patients, sulfonylurea administration in combination with insulin injections is not followed by a significant change in HGP. Possible effects of sulfonylureas on glucagon secretion and on the metabolism of free fatty acids (FFAs) may also contribute to improved sensitivity of the liver to the suppressive action of insulin, since these agents appear to reduce plasma glucagon and FFA concentrations. Thus, present data support an extrapancreatic action of sulfonylureas on the liver. However, it does appear that a certain degree of residual insulin secretion is required for sulfonylurea agents to elicit their hepatic effect.

Modulation of hepatic glucose production by non-esterified fatty acids in type 2 (non-insulin-dependent) diabetes mellitus

To study the effect of changes in plasma non-esterified fatty acid concentration on suppression of hepatic glucose production by insulin eight Type 2 (non-insulin-dependent) diabetic patients participated in three euglycaemic, hyperinsulinaemic (108pmol.m2-1.min-1) clamp studies combined with indirect calorimetry and infusion of [3-3H]-glucose and [1-14C]palmitate; (1) a control experiment with infusion of NaCl 154 mmol/l, (2) heparin was infused together with insulin, and (3) an antilipolytic agent, Acipimox, was administered at the beginning of the experiment. Six healthy volunteers participated in the control experiment. Plasma non-esterified fatty acid concentrations during the insulin clamp were in diabetic patients: (1) 151 +/- 36 mumol/l, (2) 949 +/- 178 mumol/l, and (3) 65 +/- 9 mumol/l; in healthy control subjects 93 +/- 13 mumol/l. Non-esterified fatty acid transport rate, oxidation and non-oxidative metabolism were significantly higher during the heparin than during the Acipimox experiment (p less than 0.001). Suppression of hepatic glucose production by insulin was impaired in the diabetic compared to control subjects (255 +/- 42 vs 51 +/- 29 mumol/min, p less than 0.01). Infusion of heparin did not affect the suppression of hepatic glucose production by insulin (231 +/- 49 mumol/min), whereas Acipimox significantly enhanced the suppression (21 +/- 53 mumol/min, p less than 0.001 vs 154 mmol/l NaCl experiment). We conclude that insulin-mediated suppression of hepatic glucose production is not affected by increased non-esterified fatty acid availability. In contrast, decreased non-esterified fatty acid availability enhances the suppression of hepatic glucose production by insulin.

Mechanisms of the glucose lowering effect of a carnitine palmitoyl transferase inhibitor in normal and diabetic rats

To determine the respective part of modifications of glucose appearance and disappearance rates in the hypoglycemic action of a compound (B 827-33) inhibiting carnitine palmitoyl transferase (CPT I), we measured glucose kinetics ([6,6(2)H2]glucose) in normal and diabetic (streptozocin) rats before and after injection of either saline or B 827-33. Studies were initiated 4 hours (postabsorptive groups) and 24 hours (fasted groups) after food withdrawal. In all groups, there was evidence of inhibition of fatty acids oxidation (sharp decrease of ketone bodies [KB] and increase of plasma nonesterified fatty acids [NEFA]) after B 827-33 injection. Glucose levels decreased also in all groups after B 827-33 administration, the decrease being more important in starved than in postabsorptive groups and, whatever the nutritional status, in diabetic than in normal rats. In all groups, the evolution of plasma insulin was comparable after saline or B 827-33 injection. The mechanisms responsible for the decrease in glucose levels appeared dependent on the nutritional status. In postabsorptive normal and diabetic rats, compared with saline-injected rats, we observed a moderate inhibitory action (P less than .05) of B 827-33 on glucose production without stimulation of glucose utilization rate. After 24 hours of starvation, the decrease in glucose levels of normal rats was entirely due to a stimulation of glucose utilization (P less than .05), whereas glucose production was unexpectedly increased (P less than .05) above values of saline-injected rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Fatty acid distribution in systems modeling the normal and diabetic human circulation. A 13C nuclear magnetic resonance study

A nonperturbing 13C nuclear magnetic resonance (NMR) method was used to monitor the equilibrium distribution of carboxyl 13C-enriched fatty acids (FA) between distinct binding sites on human serum albumin, native human lipoproteins, and/or phospholipid model membranes, under conditions that mimic the normal and diabetic human circulation. Two variables pertinent to the diabetic circulation were examined: FA/albumin mole ratio (as elevated in insulin deficiency and/or nephrosis) and pH (as decreased in acidosis). 13C NMR spectra for samples containing carboxyl 13C-enriched palmitate, human serum albumin, and phospholipid vesicles or native lipoproteins (all samples at pH 7.4, 37 degrees C) exhibited up to six carboxyl NMR resonances corresponding to FA bound to distinct binding sites on albumin and nonalbumin components. When the sample FA/albumin mole ratio was 1, three FA carboxyl resonances were observed (182.2, 181.8, and 181.6 ppm; designated peaks beta, gamma, and beta', respectively). These resonances corresponded to FA bound to three distinct high-affinity binding sites on human serum albumin. When the sample mole ratio value exceeded 1, additional carboxyl resonances corresponding to FA bound to phospholipid vesicles (179.0 ppm, peak phi), lipoproteins (180.7 ppm, peak sigma), and lower affinity sites on albumin (183.8 ppm, peak alpha; 181.9 ppm, peak gamma'), were observed. The intensity of peaks phi and sigma increased with increasing mole ratio or decreasing pH. Using Lorentzian lineshape analysis, the relative mole quantities of FA bound to albumin and nonalbumin binding sites were determined. Plots of the fraction of FA associated with nonalbumin components as a function of FA/albumin mole ratio were linear and extrapolated to the abscissa at a mole ratio value of 1. This pattern of FA distribution was observed regardless of the type of nonalbumin acceptor used (phospholipid vesicles, human high- or low-density lipoproteins) or the type of FA used (palmitate, oleate, or stearate), and provided evidence for negative cooperativity for human serum albumin upon binding of 1 mol of FA per mole albumin. These in vitro NMR results suggest that the threshold FA/albumin mole ratio value for alterations in FA distributions in the human circulation may be 1, rather than 3, as previously held. The pathophysiological implications of these findings are discussed.