Prolonged activation of the branched-chain α-keto acid dehydrogenase complex in muscle of zymosan treated rats

Abstract. Whole-body oxidation rates of branched chain amino acids (BCAA) are increased during catabolic diseases. A significant role for muscle in this feature has been suggested and, therefore, activities of the rate limiting enzyme in the degrada-tive pathway of the BCAA in muscle were investigated in a catabolic rat model (intraperitoneal zymosan injection). Both actual and total activities of the branched chain α-keto acid dehydrogenase complex (BC-complex) were measured in skeletal muscle of zymosan treated rats and compared with values measured in pair fed and ad libitum fed controls. The actual activity and the percentage of the enzyme in the active form were increased 2 and 6 days after the zymosan challenge. Total activity of the BC-complex and the activities of mitochondrial marker enzymes were reduced 2 days after zymosan treatment. We conclude that zymosan treatment leads to (1) a reduction of the mitochondrial content in skeletal muscle and (2) a prolonged activation of the BC-complex in muscle which may explain enhanced oxidation of BCAA during catabolic diseases.     

Hyperglycemia normalizes insulin-stimulated skeletal muscle glucose oxidation and storage in noninsulin-dependent diabetes mellitus.

The diminished ability of insulin to promote glucose disposal and storage in muscle has been ascribed to impaired activation of glycogen synthase (GS). It is possible that decreased glucose storage could occur as a consequence of decreased glucose uptake, and that GS is impaired secondarily. Muscle glucose uptake in 15 diabetic subjects was matched to 15 nondiabetic subjects by maintaining fasting hyperglycemia during infusion of insulin. Leg muscle glucose uptake, glucose oxidation (local indirect calorimetry), release of glycolytic products, and muscle glucose storage, as well as muscle GS and pyruvate dehydrogenase (PDH) were determined before and during insulin infusion. Basal leg glucose oxidation and PDH were increased in the diabetics. Insulin-stimulated leg glucose uptake in the diabetics (8.05 +/- 1.41 mumol/[min.100 ml leg tissue]) did not differ from controls (5.64 +/- 0.37). Insulin-stimulated leg glucose oxidation, nonoxidized glycolysis, and glucose storage (2.48 +/- 0.27, 0.68 +/- 0.15, and 5.04 +/- 1.34 mumol/[min.100 ml], respectively) were not different from controls (2.18 +/- 0.12, 0.62 +/- 0.16, and 2.83 +/- 0.31). PDH and GS in noninsulin-dependent diabetes mellitus (NIDDM) were also normal during insulin infusion. When diabetics were restudied after being rendered euglycemic by overnight insulin infusion, GS and PDH were reduced compared with hyperglycemia. Thus, fasting hyperglycemia is sufficient to normalize insulin-stimulated muscle glucose uptake in NIDDM, and glucose is distributed normally to glycogenesis and glucose oxidation, possibly by normalization of GS and PDH.     

Altered fiber distribution and fiber-specific glycolytic and oxidative enzyme activity in skeletal muscle of patients with type 2 diabetes

OBJECTIVE: We investigated whether alterations of glycolytic and oxidative enzyme capacity in skeletal muscle of patients with type 2 diabetes pertain to specific muscle fibers and are associated with changes in muscle fiber composition. RESEARCH DESIGN AND METHODS: Vastus lateralis muscle was obtained by percutaneous biopsy from 10 patients with type 2 diabetes and 15 age- and BMI-matched healthy volunteers. Using cytophotometry, muscle fiber composition and fiber type-specific glycolytic and oxidative enzyme activities were measured in slow oxidative, fast oxidative glycolytic, and fast glycolytic fibers. RESULTS: In the whole muscle, oxidative activity was decreased in patients with type 2 diabetes. The slow oxidative fiber fraction was reduced by 16%, whereas the fast glycolytic fiber fraction was increased by 49% in skeletal muscle from the diabetic patients. Both oxidative and glycolytic enzyme activities were significantly increased in fast glycolytic and fast oxidative glycolytic fibers of type 2 diabetic patients. However, the fiber-specific ratio of glycolytic enzyme activity relative to oxidative activity was not different between type 2 diabetic patients and the control subjects. The myofibrillic ATP activity was significantly lower in all fiber types of patients with type 2 diabetes and correlates with glucose infusion rate during the steady state of a euglycemic-hyperinsulinemic clamp and maximal aerobic capacity and negatively with HbA(1c) values. CONCLUSIONS: Reduced oxidative enzyme activity in muscle of type 2 diabetic patients is most likely due to a reduction in slow oxidative fibers. Increased glycolytic and oxidative enzyme activities in individual muscle fibers are closely related to measures of long-term glycemic control and whole-body insulin sensitivity and could therefore represent a compensatory mechanism of the muscle in function of the altered glucose metabolism.     

Muscle adaptations and glucose control after physical training in insulin-dependent diabetes mellitus

Summary. Six men and three women with insulin-dependent diabetes (without complications) participated in physical training three times a week for 20 weeks. Physical training did not change the concentration of fasting blood-glucose, glucose excretion in urine or glucosylated haemoglobin (Hb_A1). However, the glucose disposal rate during euglycaemic clamp increased after training. In two patients a minor reduction of insulin dosage was necessary to alleviate slight hypoglycaemic episodes. The training resulted in significant increases in quadriceps isometric and dynamic strength and endurance. Maximal oxygen uptake increased by 8%, the activity of glycolytic enzymes in vastus lateralis muscle by 47% for hexokinase, and 30% for tri-osephosphate dehydrogenase and 25% for lactic dehydrogenase, the activity of oxidative enzymes by 42% for citrate synthase and 46% for 3-hydroxy-acyl-CoA-dehydrogenase. The glycogen concentration in the vastus lateralis muscle did not change significantly. Lipoprotein lipase activity did not change in muscle, nor in adipose tissue. The mean muscle fibre area increased by 25% and the area of FTa fibres by 30%. The new formation of capillaries around different muscle fibres was significant for FTb fibres (26%). The proliferation of capillaries, however, appeared to be insufficient to cope with the increased area of muscle fibres. As a result, the mean area of muscle fibre supplied by one capillary (a measure of diffusion distance) significantly increased after training for FTa fibres. It is concluded that with the exception of deficient proliferation of capillaries, patients with insulin-dependent diabetes mellitus show a normal central and peripheral adaptation to physical training. Physical training does not apparently improve blood glucose control in most cases, despite an increased insulin sensitivity.     

Skeletal muscle utilization of free fatty acids in women with visceral obesity.

Visceral obesity is strongly associated with insulin resistance. One potential cause is increased availability of FFA. Alternatively, it has been proposed that there is impaired oxidation of lipid in individuals at risk for obesity. The extent to which either concept involves skeletal muscle is uncertain. To examine these opposing hypotheses, 17 healthy lean and obese premenopausal women, among whom cross-sectional area of visceral fat ranged from 18 to 180 cm2, participated in leg balance studies for measurement of FFA and glucose utilization during basal and insulin-stimulated conditions. A metabolic profile of skeletal muscle, based on enzyme activity, was determined in vastus lateralis muscle obtained by percutaneous biopsy. Visceral fat content was negatively correlated with insulin sensitivity (rates of leg glucose uptake and storage), but insulin resistance was not caused by glucose-FFA competition. During hyperinsulinemia, neither leg FFA uptake nor oxidation was increased in women with visceral obesity. During fasting conditions, however, rates of FFA uptake across the leg were negatively correlated with visceral adiposity as were activities of muscle carnitine palmitoyl transferase and citrate synthase. In summary, visceral adiposity is clearly associated with skeletal muscle insulin resistance but this is not due to glucose-FFA substrate competition. Instead, women with visceral obesity have reduced postabsorptive FFA utilization by muscle.     

Insulin treatment increases skeletal muscle fibre area in patients with diabetes mellitus type 2

The effects of insulin treatment on skeletal muscle characteristics were studied in 18 patients (62 ± 11 years) with poorly controlled diabetes mellitus type 2 (mean duration 7·5 ± 6 years). Skeletal muscle biopsy samples were taken from the lateral portion of the quadriceps muscle before and after a period of insulin treatment of 40 ± 14 days. Enzyme activities (phosphofructokinase, 3‐hydroxyacyl‐CoA dehydrogenase, citrate synthase, lactate dehydrogenase and creatine kinase) and myoglobin content were assessed. In a subgroup of 11 patients (60 ± 11 years), skeletal muscle fibre type composition (type I, IIA, IIB and IIC) and fibre type cross‐sectional area were also analysed. Following insulin treatment there were 32 and 38% increases, respectively, in the cross‐sectional areas of type IIA and IIB fast‐twitch fibres (P<0·02). The fibre type distribution did not change. The myoglobin content in muscle decreased by 20% (P<0·01). Of the enzymes tested, the 3‐hydroxyacyl‐CoA dehydrogenase activity decreased by 10% (P<0·04). Serum glucose, HbA1_C and serum triglyceride levels decreased (P<0·001) and body weight and arm muscle circumference increased (P<0·02). In conclusion, insulin treatment of patients with poorly controlled non‐insulin‐dependent diabetes mellitus increased the fast‐twitch fibre area, reduced myoglobin levels and decreased muscle enzyme activity related to fatty acid oxidation.     

Insulin Sensitivity of Forearm Tissues in Prediabetic Man

In genetic prediabetic subjects (the glucose tolerant offspring of two diabetic parents or the identical twin of a known diabetic) serum insulin concentrations after glucose administration are subnormal. Maintenance of glucose tolerance in this setting is apparently paradoxical, suggesting increased tissue insulin sensitivity. Accordingly, forearm tissue insulin sensitivity in nine genetic prediabetic males was compared with that of seven males without familial diabetes. Diabetes was excluded in all subjects by preliminary oral glucose tolerance testing.On the preliminary 3 h oral glucose tolerance test (OGTT) the sum of increments in blood glucose above fasting was greater in prediabetic than in control subjects. Conversely, the sum of increments in serum insulin was subnormal for the first 2 h. The insulin index (the sum of increments in insulin divided by the sum of increments in glucose) was significantly lower in prediabetics throughout the test. High physiologic levels of insulin were produced in the forearm by intrabrachial arterial insulin infusion (100 muU/kg per min for 26 min). Balances of glucose and amino acids across forearm muscle became more positive, as did balances of glucose and free fatty acids across adipose tissue plus skin. There were no differences in response between prediabetic and normal subjects.Hence, the insulin sensitivity of peripheral tissues is normal in genetic prediabetes. Increased tissue insulin sensitivity is not essential to explain coexisting euglycemia and insulinopenia in prediabetes because blood glucose values on the OGTT are, in fact, elevated although still within the range considered normal.     

Elevated activity of semicarbazide-sensitive amine oxidase in blood from patients with skeletal metastases of prostate cancer.

The semicarbazide-sensitive amine oxidases constitute a group of copper-containing enzymes whose physiological function is unclear. The enzymes are present in various tissues, including blood plasma. At present, the source of the plasma enzyme in humans is not known. Results of a recent study suggested that semicarbazide-sensitive amine oxidase is expressed in the skeleton, e.g. in the spine. Using an indirect autoradiographic method in mice, we provide evidence that semicarbazide-sensitive amine oxidase is present in high abundance in bone tissue. Specific activities of semicarbazide-sensitive amine oxidase were estimated in blood samples from subjects with femoral bone fractures. Moreover, enzyme activities were also measured in patients suffering from prostate cancer with skeletal metastases. The level of specific semicarbazide-sensitive amine oxidase activity in serum was significantly elevated in patients with skeletal metastases compared with both healthy controls and patients having prostate cancer without signs of skeletal metastases. Based on the results of the present study, we propose that semicarbazide-sensitive amine oxidase in blood plasma may originate, at least in part, from the skeleton.     

低血糖对肌肉损伤影响的实验研究

目的;研究胰岛素剂量和低血糖持续时间对血清酶活性影响,确定低血糖损伤的脏器。方法：根据胰岛素剂量和低血糖持续时间的不同,将30只家兔分为5组：A2组,胰岛素2U／kg低血糖持续30min;A10组,胰岛素10U/kg低血糖持续30min;B2组,胰岛素2U／kg低血糖持续60min;B10组：胰岛素10U/kg低血糖持续60min;C对照组：胰岛素10U/kg加50％葡萄糖注射不诱发低血糖。胰岛素注射前后对血清酶的活性及肌酸激酶（CK）同功酶的分布进行观察。结果：所有低血糖组其血清CK的活性较对照组明显增高,且在A10和B10组CK活性的升高持续24h,而血清ALT、AST、LDH的升高仅见于B10组。此外,主要存在于心肌和骨骼肌中的CK－Band4在B10组可见显著升高。结论：低血糖所致血清酶活性及CK－Band4的升高是由于肌肉损伤的结果而非肝脏的损伤,低血糖持续的时间和胰岛素剂量可以影响脏器损伤的程度。     

Enzyme Activities in Skeletal Muscles from Patients with Peripheral Arterial Insufficiency

The enzyme pattern in gastrocnemius muscle tissue was studied in 3 9 patients with peripheral arterial insufficiency. Phosphofructokinase and glucose-6-phosphate-dehydroge-nase were significantly increased in the skeletal muscles from these patients. The most pronounced changes were found in 3-OH-acyl-CoA-dehydrogenase, citrate synthase, and in cytochrome-c-oxidase. These enzyme activities were increased by 60, 40 and 25 per cent respectively. In patients with claudication as the only symptom, the metabolic capacity was generally increased in skeletal muscles affected by the low blood flow. With increasing severity of arterial insufficiency, all enzyme activities decreased and glycolytic enzymes were affected first. 3-OH-acyl-CoA-dehydrògenase, citrate synthase and cytochrome-c-oxidase activities were still comparatively high in patients with gangrenous foot ulcers, indicating some maintenance of the muscle viability even in situations with very low blood flow.     

Enzyme activities in skeletal muscles from patients with peripheral arterial insufficiency.

The enzyme pattern in gastrocnemius muscle tissue was studied in 39 patients with peripheral arterial insufficiency. Phosphofructokinase and glucose-6-phosphate-dehydrogenase were significantly increased in the skeletal muscles from these patients. The most pronounced changes were found in 3-OH-acyl-CoA-dehydrogenase, citrate synthase, and in cytochrome-c-oxidase. These enzyme activities were increased by 60, 40 and 25 per cent respectively. In patients with claudication as the only symptom, the metabolic capacity was generally increased in skeletal muscles affected by the low blood flow. With increasing severity of arterial insufficiency, all enzyme activities decreased and glycolytic enzymes were affected first. 3-OH-acyl-CoA-dehydrogenase, citrate synthase and cytochrome-c-oxidase activities were still comparatively high in patients with gangrenous foot ulcers, indicating some maintenance of the muscle viability even in situations with very low blood flow.     

Fatty acyl-CoA dehydrogenase enzymes in human skeletal muscle

An electrophoretic and enzyme-substrate staining technique for acyl-CoA dehydrogenase (ACD) enzymes was developed for use with small (less than 100 mg) tissue samples. Based on their electrophoretic mobility and substrate staining specificity, at least two and perhaps three chain-length specific enzymes for dehydrogenation of saturated fatty acids were found in human skeletal muscle. ACD enzymes staining with octanoyl-CoA or palmitoyl-CoA were identified by this technique in human skeletal muscle, heart, and liver, but the ACD enzyme staining with butyryl-CoA was difficult to detect and was definitely visualized only in skeletal muscle.     

Mechanisms of insulin resistance in cancer associated malnutrition

Summary. This study has evaluated insulin resistance under steady-state conditions using the glucose clamp technique. Euglycaemic clamp investigations were conducted at 4–5 different insulin levels (70–1600 mUl^-1) in five malnourished cancer patients, four well-nourished Intensive Care Unit patients (ICU) and 11 well-nourished individuals. Whole body uptake of glucose was measured. In three cancer patients the flux of glucose across the leg was measured. Cancer patients had significantly reduced fasting insulin concentrations, while ICU patients had increased levels compared to controls. The fasting levels of glucose did not differ among the groups. Both insulin sensitivity and responsiveness were reduced by 50% in cancer and ICU patients. At insulin levels of 200–250 mUl^-1, approximately 80% of the whole body glucose uptake could be accounted for by the peripheral tissues. This study confirms that insulin resistance is a significant metabolic alteration in cancer associated malnutrition. The results demonstrate both decreased insulin sensitivity and responsiveness.     

56例肝癌患者血糖、胰岛素与C肽水平分析

目的探讨肝癌患者的血糖、胰岛素与C肽水平变化。方法回顾分析56例肝癌患者及48例正常对照者空腹及口服75g葡萄糖后1、2、3h的血糖、胰岛素与C肽水平。结果与正常对照组比较,肝癌组空腹血糖差异无统计学意义（P〉O．05）,服糖后1、2、3h血糖均呈显著性升高,差异有统计学意义（P〈O．01）;空腹血清胰岛素呈显著性升高,差异有统计学意义（P〈O．01）,服糖后1h血清胰岛素呈显著性降低（P〈O．01）,服糖后2、3h血清胰岛素呈显著性升高,差异有统计学意义（P〈O．01）;空腹血清C肽差异无统计学意义（P〉O．05）,但服糖后1、2、3h血清C肽均呈显著性升高,差异有统计学意义（P〈O．01）。结论肝癌患者糖代谢异常主要表现为糖耐量降低、高胰岛素血症、胰岛素分泌延缓与消除延迟、服糖后高C肽血症。     

Isokinetic strength training protocols: do they induce skeletal muscle fiber hypertrophy?

Sedentary subjects were submitted to repeated concentric isokinetic strength training protocols separated by a 50-day detraining period. Peak torque output of the quadriceps muscle group increased by 54% after the first ten-week training protocol. No significant changes in mean skeletal muscle fiber area were observed while a significant increase in percent fiber type and percent fiber area was noticed for type IIa fibers. The activities of the enzymes hexokinase, malate dehydrogenase, 3-hydroxyacyl CoA dehydrogenase, and oxoglutarate dehydrogenase were also increased significantly. Fifty days without training induced a significant decline in peak torque output. All the enzymes that responded to the first training protocol maintained their elevated activities over the detraining period except for the enzyme oxoglutarate dehydrogenase. A second training protocol administered to the same subjects following the 50-day inactivity period did not result in any significant increase in maximum torque output and fiber area. It is concluded that the isokinetic strength training protocol used can increase the functional capacity of skeletal muscle, but this effect does not appear to be related to skeletal muscle fiber hypertrophy.     

Effects of insulin infusion on human skeletal muscle pyruvate dehydrogenase, phosphofructokinase, and glycogen synthase. Evidence for their role in oxidative and nonoxidative glucose metabolism.

To determine whether activation by insulin of glycogen synthase (GS), phosphofructokinase (PFK), or pyruvate dehydrogenase (PDH) in skeletal muscle regulates intracellular glucose metabolism, subjects were studied basally and during euglycemic insulin infusions of 12, 30, and 240 mU/m2 X min. Glucose disposal, oxidative and nonoxidative glucose metabolism were determined. GS, PFK, and PDH were assayed in skeletal muscle under each condition. Glucose disposal rates were 2.37 +/- 0.11, 3.15 +/- 0.19, 6.71 +/- 0.44, and 11.7 +/- 1.73 mg/kg X min; glucose oxidation rates were 1.96 +/- 0.18, 2.81 +/- 0.28, 4.43 +/- 0.32, and 5.22 +/- 0.52. Nonoxidative glucose metabolism was 0.39 +/- 0.13, 0.34 +/- 0.26, 2.28 +/- 0.40, and 6.52 +/- 1.21 mg/kg X min. Both the proportion of active GS and the proportion of active PDH were increased by hyperinsulinemia. PFK activity was unaffected. Activation of GS was correlated with nonoxidative glucose metabolism, while activation of PDH was correlated with glucose oxidation. Sensitivity to insulin of GS was similar to that of nonoxidative glucose metabolism, while the sensitivity to insulin of PDH was similar to that of glucose oxidation. Therefore, the activation of these enzymes in muscle may regulate nonoxidative and oxidative glucose metabolism.     

Impaired glucose homeostasis in insulin-like growth factor binding protein-1 transgenic mice.

Transgenic mice that overexpressed IGFBP-1 are hyperinsulinemic in the first week of life and gradually develop fasting hyperglycemia. In adult transgenic mice, the hypoglycemic response to IGF-I but not insulin or des (1-3) IGF-I was attenuated (P < 0.05) compared with wild-type mice. Furthermore, in isolated adipocytes from transgenic mice, the stimulatory effect of IGF-I but not insulin on 2-deoxy-[3H]-glucose uptake was reduced (P < 0.02). In contrast, in isolated soleus muscle, the effects of both IGF-I and insulin on 2-deoxy-3H-glucose uptake and on [3H]-glucose incorporation into glycogen were significantly reduced compared to wild-type mice. The decline in specific activity of the 2-deoxy-3H-glucose, a measure of glucose appearance in the circulation, was more marked in transgenic animals (P < 0.05). In addition, tissue uptake of glucose was significantly higher in diaphragm, heart, intestine, liver, soleus muscle, and adipose tissue from fasting transgenic mice. Plasma concentrations of alanine, lysine, and methionine were also elevated in transgenic mice. These data suggest that overexpression of IGFBP-1 attenuates the hypoglycemic effect of endogenous IGF-I, which is initially compensated for by enhanced pancreatic insulin production. However, in adult mice pancreatic insulin content is reduced, insulin resistance is demonstrable in skeletal muscle and fasting hyperglycemia develops.     

Insulin and glucose uptake and insulin sensitivity in patients with peripheral arterial insufficiency

Abstract. There have been previous reports of evidence for increased insulin sensitivity in patients with intermittent claudication as the only symptom of arterial insufficiency. This study was designed to evaluate the role of peripheral tissue with respect to insulin sensitivity in such patients. Intravenous glucose tolerance tests (IVGTT) and intravenous insulin tolerance tests (IVITT) were performed in patients with peripheral arterial insufficiency and in controls. During IVGTT the plasma insulin values were significantly lower in patients with arterial insufficiency. During IVITT the venous concentration of glucose decreased more and the area over the glucose curve was significantly larger, suggesting a higher insulin sensitivity in this group. The low insulin values could not be referred to a larger distribution volume or an increased degradation rate, suggesting decreased pancreatic insulin release in this group. At the time of surgery for arterial insufficiency and for varicose veins in controls, the uptake of insulin and glucose and the release of lactate were measured over the leg before and after a glucose load. The uptake of insulin over the leg correlated positively with the arterial insulin concentration and the uptake of glucose in both groups. The insulin uptake had a tendency to be increased in legs with arterial insufficiency during the glucose challenge. The glucose uptake in the leg did not differ in the basal state, but was 3 times higher in the legs of patients with arterial insufficiency during glucose challenge. The increased glucose uptake in this group could be ascribed to a high insulin sensitivity in the leg, as defined by glucose uptake per unit of insulin taken up.     

正电子发射断层成像/CT观察健康人空腹时不同器官对~（18）F脱氧葡萄糖的摄取

背景：既往国内外研究中,主要针对肿瘤患者体内葡萄糖的摄取情况,而关于正常人在空腹状态下不同器官对葡萄糖的摄取作用研究很少。目的：正电子发射断层成像/CT观察健康人在空腹状态下不同器官对18F脱氧葡萄糖的摄取情况,分析空腹时脑、肝、肾、心脏和骨骼肌组织在糖代谢中的相关性。方法：31例健康成年人空腹抽血测肝肾功能、血糖和血脂,并行正电子发射断层成像/CT检查,测脑、心脏、肝、肾脏和骨骼肌的18F脱氧葡萄糖的平均标准摄入值以及最大标准摄入值。结果与结论：空腹时脑皮质18F脱氧葡萄糖的平均标准摄入值约是心脏和肾脏的两三倍,是肝脏的4倍左右,是骨骼肌的15倍。肝脏平均标准摄入值与肾脏和骨骼肌的平均标准摄入值呈显著正相关（r=0.406,0.391,P=0.023,0.030）,但肝脏的平均标准摄入值与心和脑的平均标准摄入值无相关性。结果提示空腹状态下脑组织对葡萄糖摄取最多,骨骼肌最少,心脏、肝脏和肾脏居中;空腹状态下肝脏与肾脏和骨骼肌之间对葡萄糖的代谢存在显著相关性。