Diabetic Adipose Tissue Research Articles

Abstract 207: Reduced Vascular Density in Human Adipose Tissue in Diabetes is Associated with Reduced Angiogenesis and De-differentiation of Endothelial Cells

Emerging evidence suggests that impaired adipose tissue (AT) angiogenesis leads to metabolic dysfunction. The de-differentiation of endothelial cells (EC) into a mesenchymal phenotype (EndoMT) in AT vasculature could be a potential contributor to dysfunctional EC including impaired angiogenesis. One of the major drivers of EndoMT is TGF, and both macrophages and T cells infiltrating AT in obesity could contribute to EndoMT via TGF production. The objective of this project was to characterize angiogenesis and the EC phenotype in human AT vasculature. We examined functional angiogenesis and gene expression in omental (OM) AT from obese T2D subjects (BMI>33, HbA1c>6.5%) and non-diabetic (ND) subjects (BMI>33). Sprouting angiogenesis of AT explants embedded in matrigel was 1.5-fold higher in ND vs. T2D (p<0.05). Also, capillary and arteriolar density assessed as CD31 and α-SMC immuno-positivity, was 2-fold higher in ND vs. T2D. Using a Human Angiogenesis PCR Array we found that in T2D vs. ND OM AT, there was >2-fold down-regulation in expression of genes involved in cell proliferation and matrix remodeling (JAG, ID1, COL4A3, TIMP1 and CTGF) (p<0.05). In conclusion, in T2D in obesity there is a reduction in vascular density that can be explained in part by the reduced angiogenic potential. Next, we tested the hypothesis that a potential contributor to reduced angiogenesis is de-differentiation of EC in AT vasculature. We determined the molecular phenotype of EC isolated from human AT. Indeed, EC (CD34 + 31 + ) isolated from ND and T2D obese AT had significantly >10-fold up-regulation of mesenchymal genes (TGF-β, fibroblast specific protein-1 (FSP1), and Twist1) compared to dermal human microvascular endothelial cells (HMVEC) (p<0.001). Also, EC isolated from AT displayed a prominent oxidative metabolism compared to dermal HMVEC that utilized primarily glycolysis. This phenotype was similar to the one of TGF treated dermal HMVEC. Since glycolysis is required for angiogenic ECs, the low glycolytic flux of AT EC could contribute to impaired angiogenesis. In conclusion, EC isolated from obese and T2D patients show increased expression of mesenchymal markers and a metabolic shift towards the oxidative metabolism, which may explain reduced angiogenesis.

Hyperglycemia diverts dividing stem cells to pathological adipogenesis.

This commentary proposes a mechanism for why murine diabetic adipose tissue contains very few remaining stem cells compared with normal adipose tissue. The mechanism involves the diversion of stem cells to pathological adipocytes when they divide in hyperglycemia.

Enhanced ROS production and oxidative damage in subcutaneous white adipose tissue mitochondria in obese and type 2 diabetes subjects.

Oxidative stress in the insulin target tissues has been implicated in the pathophysiology of type 2 diabetes. The study has examined the oxidative stress parameters in the mitochondria of subcutaneous white adipose tissue from obese and non-obese subjects with or without type 2 diabetes. An accumulation of protein carbonyls, fluorescent lipid peroxidation products, and malondialdehyde occurs in the adipose tissue mitochondria of obese type 2 diabetic, non-diabetic obese, and non-obese diabetic subjects with the maximum increase noticed in the obese type 2 diabetes patients and the minimum in non-obese type 2 diabetics. The mitochondria from obese type 2 diabetics, non-diabetic obese, and non-obese type 2 diabetics also produce significantly more reactive oxygen species (ROS) in vitro compared to those of controls, and apparently the mitochondrial ROS production rate in each group is proportional to the respective load of oxidative damage markers. Likewise, the mitochondrial antioxidant enzymes like superoxide dismutase and glutathione peroxidase show decreased activities most markedly in obese type 2 diabetes subjects and to a lesser degree in non-obese type 2 diabetes or non-diabetic obese subjects in comparison to control. The results imply that mitochondrial dysfunction with enhanced ROS production may contribute to the metabolic abnormality of adipose tissue in obesity and diabetes.

Phosphatase and tension homolog overexpression in insulin resistant diabetic adipose tissue.

To investigate the expression of phosphatase and tension homolog (PTEN) in adipose tissue of KKAy diabetic mice, a mouse model of type 2 diabetes. KKAy diabetic mice were fed with high fat diet for 4 weeks. After blood glucose met the criteria of diabetes (over 16.7 mmol/L), mice were randomly divided into 3 groups: a control group (without any treatment), a rosiglitazone group (treated with rosiglitazone 12.5 mg/kg.d once per day), and a metformin group (treated with metformin 3 g/kg.d twice daily). After 4 weeks, we then determined the expression of PTEN and phosphoserine 473-Akt (pS473-Akt) in the epididymal adipose tissue with Western blots. The mice in each group were further divided into the insulin (-) subgroup and insulin (+) subgroup, which were intraperitoneally injected with saline and insulin (5 mU/g body weight), respectively. The expression of PTEN was elevated in the epididymal adipose tissue obtained from KKAy diabetic mice compared with that from the C57BL/6J mice (P<0.001). In accordance with the enhanced expression of PTEN, the level of pS473-Akt stimulated by insulin was decreased in the adipose tissue of KKAy mice compared to the C57BL/6J mice (P<0.001). Treatment with the insulin-sensitizing agents, rosiglitazone and metformin did not inhibit the elevated expression of PTEN in adipose tissue of KKAy diabetic mice. PTEN may play an important role in the development of insulin resistance in adipose tissue of type 2 diabetes mice model.

The succinated proteome

The post-translational modifications (PTMs) of cysteine residues include oxidation, S-glutathionylation, S-nitrosylation, and succination, all of which modify protein function or turnover in response to a changing intracellular redox environment. Succination is a chemical modification of cysteine in proteins by the Krebs cycle intermediate, fumarate, yielding S-(2-succino)cysteine (2SC). Intracellular fumarate concentration and succination of proteins are increased by hyperpolarization of the inner mitochondrial membrane, in concert with mitochondrial, endoplasmic reticulum (ER) and oxidative stress in 3T3 adipocytes grown in high glucose medium and in adipose tissue in obesity and diabetes in mice. Increased succination of proteins is also detected in the kidney of a fumarase deficient conditional knock-out mouse which develops renal cysts. A wide range of proteins are subject to succination, including enzymes, adipokines, cytoskeletal proteins, and ER chaperones with functional cysteine residues. There is also some overlap between succinated and glutathionylated proteins, suggesting that the same low pKa thiols are targeted by both. Succination of adipocyte proteins in diabetes increases as a result of nutrient excess derived mitochondrial stress and this is inhibited by uncouplers, which discharge the mitochondrial membrane potential (ΔΨm) and relieve the electron transport chain. 2SC therefore serves as a biomarker of mitochondrial stress or dysfunction in chronic diseases, such as obesity, diabetes, and cancer, and recent studies suggest that succination is a mechanistic link between mitochondrial dysfunction, oxidative and ER stress, and cellular progression toward apoptosis. In this article, we review the history of the succinated proteome and the challenges associated with measuring this non-enzymatic PTM of proteins by proteomics approaches.

The association of adipose-derived dimethylarginine dimethylaminohydrolase-2 with insulin sensitivity in experimental type 2 diabetes mellitus

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase (NOS), which can be hydrolyzed by dimethylarginine-dimethylaminohydrolase (DDAH). It has been reported that adipocytes can produce DDAH/ADMA, but its role remains unknown. In the present study, we examined the effects of adipocyte-derived DDAH/ADMA on insulin sensitivity using animal and cell models. Results showed that in adipose tissue of high fat diet-fed diabetic rats, as well as in high glucose (25 mM) plus insulin (100 nM)-treated 3T3-L1 adipocytes, expression levels of insulin receptor substance-1 (IRS-1), glucose transporter-4 (GLUT-4), and DDAH isoform-2 (DDAH-2) were down-regulated compared with control, although DDAH-1 expression showed no significant changes. We also observed that nitric oxide bioavailability, DDAH and NOS activities were subsequently decreased, while the local ADMA content was elevated in diabetic adipose tissue. Transfection of human DDAH-2 gene into high glucose- and insulin-treated 3T3-L1 adipocytes significantly ameliorated DDAH activity, reduced ADMA contents, and up-regulated the mRNA expression levels of IRS-1 and GLUT-4. These findings suggested that in the development of type 2 diabetes mellitus, local DDAH-2 in adipocytes might play an important role in regulating insulin sensitivity.

Streptozotocin으로 당뇨가 유도된 C57BL/6 생쥐 지방조직에서의 염증성 사이토카인 유전자의 이상발현

본 연구를 통하여 streptozotocin 주사에 의한 당뇨 유발이 일반식이와 고지방식이로 키운 C57BL/6 수컷생쥐의 지방조직에서의 염증성 사이토카인 유전자 발현에 미치는 영향을 조사하였다. 네 그룹의 당뇨생쥐(일반식이 또는 고지방식이로 키운 16주령 또는 26주령 생쥐)와 네 그룹의 비당뇨 대조군을 포함한 모두 73마리의 생쥐가 이 실험에 사용되었다. Real-time PCR을 이용하여 지방조직에서의 tumor necrosis factor-<TEX>${\alpha}$</TEX> (TNF-<TEX>${\alpha}$</TEX>)와 monocyte chemoattractant protein-1 (MCP-1)의 유전자 발현량을 측정한 결과, TNF-<TEX>${\alpha}$</TEX> mRNA는 당뇨 유발에 의해 증가하는 양상을 보였다. 특히, 16주령의 일반식이 생쥐의 경우 비당뇨 대조군에 비해 당뇨가 유발된 실험군에서 유의한 증가가 관찰되었다. MCP-1 mRNA 발현은 STZ처리에 따른 당뇨유발에 의해 감소하는 경향을 나타내었다. 특히, 16주령 고지방식이의 당뇨 실험군에서의 발현이 비당뇨 대조군에서의 발현량의 26%에 해당할 정도로 큰 감소를 나타내었다. 또한, MCP-1의 발현은 인슐린 농도와 유의한 상관관계가 있음이 확인되었다. 이들 실험결과는 당뇨 모델 생쥐에서 지방조직의 염증성 사이토카인이 이상발현되고 있음을 나타내며, 비만, 인슐린저항성, 및 당뇨에서의 저준위 염증상태와 지방조직에서의 염증성 사이토카인 발현 조절의 기작을 밝히는데 유용한 정보를 제공할 것으로 기대된다. The aim of this study was to investigate the effects of induced diabetes by streptozotocin (STZ) administration on gene expression of proinflammatory cytokines in adipose tissue of C57/BL6 mice fed either a normal diet (ND) or a high-fat diet (HFD). Four diabetic mice groups (16- or 26-week-old mice fed either ND or HFD) and four control groups of age and diet matched non-diabetic mice were used. By real-time PCR, gene expression levels of tumor necrosis factor-<TEX>${\alpha}$</TEX> (TNF-<TEX>${\alpha}$</TEX>) and monocyte chemoattractant protein-1 (MCP-1) were examined in adipose tissue. The results demonstrated that gene expression of TNF-<TEX>${\alpha}$</TEX> was significantly or marginally increased in STZ induced diabetic mice groups compared with non-diabetic groups. On the other hand, MCP-1 gene expression tended to be decreased in diabetic mice compared with non-diabetic controls. Especially, MCP-1 expression level in 16w diabetic mice on HFD was about 26% of that in age and diet matched non-diabetic controls (p<0.001). In addition, MCP-1 gene expression in adipose tissue was correlated with plasma insulin levels (p=0.0002). These results suggest that gene expression of proinflammatory cytokines in adipose tissue is differentially regulated in mouse models of diabetes. The basic data in this study will be useful for elucidating basic mechanisms of inflammatory state and increased expression of proinflammatory cytokines in adipose tissue in obesity, insulin resistance, and diabetes.

Mitochondrial stress causes increased succination of proteins in adipocytes in response to glucotoxicity

2SC [S-(2-succino)-cysteine] is a chemical modification formed by a Michael addition reaction of fumarate with cysteine residues in proteins. Formation of 2SC, termed 'succination' of proteins, increases in adipocytes grown in high-glucose medium and in adipose tissues of Type2 diabetic mice. However, the metabolic mechanisms leading to increased fumarate and succination of protein in the adipocyte are unknown. Treatment of 3T3 cells with high glucose (30mM compared with 5mM) caused a significant increase in cellular ATP/ADP, NADH/NAD+ and Δψm (mitochondrial membrane potential). There was also a significant increase in the cellular fumarate concentration and succination of proteins, which may be attributed to the increase in NADH/NAD+ and subsequent inhibition of tricarboxylic acid cycle NAD+-dependent dehydrogenases. Chemical uncouplers, which dissipated Δψm and reduced the NADH/NAD+ ratio, also decreased the fumarate concentration and protein succination. High glucose plus metformin, an inhibitor of complex I in the electron transport chain, caused an increase in fumarate and succination of protein. Thus excess fuel supply (glucotoxicity) appears to create a pseudohypoxic environment (high NADH/NAD+ without hypoxia), which drives the increase in succination of protein. We propose that increased succination of proteins is an early marker of glucotoxicity and mitochondrial stress in adipose tissue in diabetes.

Succination of Thiol Groups in Adipose Tissue Proteins in Diabetes: SUCCINATION INHIBITS POLYMERIZATION AND SECRETION OF ADIPONECTIN

S-(2-Succinyl)cysteine (2SC) is formed by reaction of the Krebs cycle intermediate fumarate with cysteine residues in protein, a process termed succination of protein. Both fumarate and succination of proteins are increased in adipocytes cultured in high glucose medium (Nagai, R., Brock, J. W., Blatnik, M., Baatz, J. E., Bethard, J., Walla, M. D., Thorpe, S. R., Baynes, J. W., and Frizzell, N. (2007) J. Biol. Chem. 282, 34219-34228). We show here that succination of protein is also increased in epididymal, mesenteric, and subcutaneous adipose tissue of diabetic (db/db) mice and that adiponectin is a major target for succination in both adipocytes and adipose tissue. Cys-39, which is involved in cross-linking of adiponectin monomers to form trimers, was identified as a key site of succination of adiponectin in adipocytes. 2SC was detected on two of seven monomeric forms of adiponectin immunoprecipitated from adipocytes and epididymal adipose tissue. Based on densitometry, 2SC-adiponectin accounted for approximately 7 and 8% of total intracellular adiponectin in cells and tissue, respectively. 2SC was found only in the intracellular, monomeric forms of adiponectin and was not detectable in polymeric forms of adiponectin in cell culture medium or plasma. We conclude that succination of adiponectin blocks its incorporation into trimeric and higher molecular weight, secreted forms of adiponectin. We propose that succination of proteins is a biomarker of mitochondrial stress and accumulation of Krebs cycle intermediates in adipose tissue in diabetes and that succination of adiponectin may contribute to the decrease in plasma adiponectin in diabetes.

INCREASED MOBILIZATION OF FREE FATTY ACIDS FROM ADIPOSE TISSUE IN DIABETES.

Increased Mobilization of Free Fatty Acids from Adipose Tissue in Diabetes Get access Nutrition Reviews, Volume 22, Issue 11, November 1964, Pages 334–337, https://doi.org/10.1111/j.1753-4887.1964.tb04834.x Published: 01 November 1964

The level and compartmentalization of phosphatidate phosphatase-1 (lipin-1) control the assembly and secretion of hepatic VLDL

Phosphatidate phosphatase-1 (PAP-1) converts phosphatidate to diacylglycerol and plays a key role in the biosynthesis of phospholipids and triacylglycerol (TAG). PAP-1 activity is encoded by members of the lipin family, including lipin-1 (1alpha and 1beta), -2, and -3. We determined the effect of lipin-1 expression on the assembly and secretion of very low density lipoproteins (VLDL) using McA-RH7777 cells. Expression of lipin-1alpha or -1beta increased the synthesis and secretion of [(3)H]glycerol-labeled lipids under either basal- or oleate-supplemented conditions. In the presence of oleate, the increased TAG secretion was mainly associated with VLDL(1) (S(f) > 100) and VLDL(2) (S(f) 20-100). Expression of lipin-1alpha or -1beta increased secretion efficiency and decreased intracellular degradation of [(35)S]apolipoprotein B-100 (apoB100). Knockdown of lipin-1 using specific short interfering RNA decreased secretion of [(3)H]glycerolipids and [(35)S]apoB100 even though total PAP-1 activity was not decreased, owing to the presence of lipin-2 and -3 in the cells. Deletion of the nuclear localization signal sequences within lipin-1alpha not only abolished nuclear localization but also resulted in impaired association with microsomal membranes. Cells expressing the cytosolic lipin-1alpha mutant failed to promote [(35)S]apoB100 synthesis or secretion, and showed compromised stimulation in [(3)H]TAG synthesis and secretion. Thus, alteration in hepatic expression of lipin-1 and its compartmentalization control VLDL assembly/secretion.

Intra-abdominal Fat Adiponectin Receptors Expression and Cardiovascular Metabolic Risk Factors in Obesity and Diabetes

The effects of adiponectin on glucose and lipid metabolism are mediated by the adiponectin receptors, adipoR1 and adipoR2, which are mainly in liver and muscle. We investigated the presence of adiponectin receptors in intra-abdominal adipose tissue (IAAT) in obesity and diabetes and their association with adiponectin expression and components of the metabolic syndrome and/or other metabolic factors associated with atherosclerotic cardiovascular disease (ASCVD). AdipoR1 and adipoR2 gene expression was measured by quantitative real time reverse transcription polymerase chain reaction in IAAT from lean and obese patients with or without diabetes type 2. Correlation between metabolic characteristics of obese patients and expression of these receptors was studied. Neither obesity nor diabetes were associated with changes in IAAT-adipoR1 expression. In contrast, IAAT-adipoR2 was decreased by 39.5% in obese non-diabetics and by 52.7% in obese diabetics when compared to lean subjects. AdipoR1 and adiponectin expression was associated in lean (r=0.943, P<0.005) and obese non-diabetic patients (r=0.74, P<0.01), whereas a positive correlation between adipoR2 and adiponectin expression was only found in the presence of diabetes (r=0.883, P<0.002). AdipoR1 expression was associated with plasma free fatty acids (FFA) concentration (r=0.76, P<0.04), and adipoR2 inversely correlated with plasma levels of triglycerides (r=-0.76, P<0.04) and apolipoprotein B (r=-0.74, P<0.05). AdipoR1 expression in IAAT was not altered by obesity and/or diabetes and was related to plasma levels of FFA. IAAT-adipoR2 expression was reduced in obesity and diabetes and associated with components of metabolic processes leading to cardiovascular disease in obesity.

Regulation of glucose utilization and lipogenesis in adipose tissue of diabetic and fat fed animals: effects of insulin and manganese.

In order to evaluate the modulatory effects of manganese, high fat diet fed and alloxan diabetic rats were taken and the changes in the glucose oxidation, glycerol release and effects of manganese on these parameters were measured from adipose tissue. An insulin-mimetic effect of manganese was observed in the adipose tissue in the controls and an additive effect of insulin and manganese on glucose oxidation was seen when Mn2+ was added in vitro. The flux of glucose through the pentose phosphate pathway and glycolysis was significantly decreased in high fat fed animals. Although the in vitro addition of Mn2+ was additive with insulin when 14CO2 was measured from control animals, it was found neither in young diabetic animals (6-8 weeks old) nor in the old (16 weeks old). Both insulin and manganese caused an increased oxidation of carbon-1 of glucose and an increase of its incorporation into 14C-lipids in the young control animals; the additive effect of insulin and manganese suggests separate site of action. This effect was decreased in fat fed animals, diabetic animals and old animals. Manganese alone was found to decrease glycerol in both the control and diabetic adipose tissue in in vitro incubations. The results of the effects of glucose oxidation, lipogenesis, and glycerol release in adipose tissue of control and diabetic animals of different ages are presented together with the effect of manganese on adipose tissue from high fat milk diet fed animals.

Activation of Cyclic Amp Phosphodiesterase by Phorbol and Protein Kinase C Pathway: Differences in Normal and Diabetic Tissue

Diabetes mellitus is associated with high levels of adenosine 3',5'-cyclic monophosphate in tissue and plasma. Diabetes inhibits and insulin stimulates and restores low Km adenosine 3',5'-cyclic monophosphate phosphodiesterase activity. We recently reported that phorbol ester, a tumor promoting agent known to act through protein kinase C also stimulates phosphodiesterase. Here, we address the issue of whether or not the activation of phosphodiesterase by insulin and phorbol ester is different in streptozotocin diabetic adipose tissue. Rat adipose tissue was incubated with insulin, phorbol ester or other known components or effectors of the protein kinase C pathway, i.e. 1,2 dioleoyl-glycerol, 1- oleoyl, 2- acetylglycerol, Ca(++)-Ionophore A 23187, and nifedipine. After incubation, preparation and assay of adenosine 3',5'-cyclic monophosphate phosphodiesterase was made. As in previous data streptozotocin-diabetes inhibits basal phosphodiesterase by about 50% (P less than .02); insulin and phorbol ester each stimulate phosphodiesterase, in streptozotocin-diabetes less than normal (P less than .025); nifedipine inhibits phorbol stimulated phosphodiesterase in streptozotocin-diabetes but not normal (P less than .001); and nifedipine inhibits insulin stimulated phosphodiesterase in normal (84%) and diabetic (97%) (P less than .005). In normal and diabetic tissue, diacyl glycerol and oleoyl-acyl glycerol stimulate phosphodiesterase, are augmented by ionophore and inhibited by nifedipine. In addition 32P incorporation studies and measurements of tyrosine kinase activity are presented which support these differences between normal and diabetic. In summary then, these data suggest common pathways of activation for low Km adenosine 3',5'-cyclic monophosphate phosphodiesterase by insulin and phorbol ester; imply a relationship between two second messenger systems, phosphoinositides and adenosine 3',5'-cyclic monophosphate; and demonstrate a difference in activation of phosphodiesterase between normal and diabetic adipose tissue.

Is copper effect on glucose incorporation mediated by the insulin receptor in rat adipose tissue?

The insulin receptor is not the site for the stimulatory effect of copper on glucose incorporation into total lipids by adipose tissue; prewashing of adipose tissue of rats fed a stock diet in an insulin-free medium increases the glucose incorporation into total lipids in the presence of 0.1 unit insulin from 220 above control to 430% in the nondiabetic and from 154 to 230% in the streptozotocin-diabetic rat. In contrast, glucose incorporation in the presence of CuCl2 X 2H2O is unaffected by prewashing, being the same in the prewashed as in the unwashed adipose tissue. On the other hand, mild trypsin digestion of adipocytes decreases the glucose incorporation in the presence of 28.5 mU insulin, from 201 to 126% - whereas the effect of copper on glucose incorporation is the same in the trypsin-treated or untreated adipocyte. In order to obtain maximal copper effect the adipocyte has to be preconditioned by insulin; preincubation of diabetic adipose tissue first for one hour with 0.1 unit insulin, and another hour with 100 micrograms CuCl2 X 2H2O added to the medium, results in greater glucose incorporation (230% above control) than when incubated alone with either CuCl2 X 2H2O (125%) or insulin (154%) for two hours. In addition to its previously noted effect on the in vivo insulin release, copper increased the number of the insulin receptor sites in adipocytes.

Biochemical characterization of ketosis-resistant young diabetics of northern India. In vivo effects of i.v. glucose, s.c. epinephrine and i.v. glucagon and in vitro effects of anti-insulin serum on adipose tissue lipolysis.

Epinephrine (10 micrograms/kg body weight) s.c., glucagon (1 microgram/kg body weight) i.v. and glucose (0.5 g/kg body weight) i.v. were injected in groups of ketosis-prone young diabetics, ketosis-resistant young diabetics, maturity-onset diabetics, young and mature controls, each group comprising 8 subjects. Samples were drawn at timed intervals and analyzed for glucose, FFA, acetone, citrate and plasma free insulin. FFA and glycerol release by the adipose tissue in vitro was studied in 6 of each of the following groups: young diabetics and young controls in the presence of norepinephrine, anti-insulin serum or both. Failure of the adipose tissue of ketosis-resistant young diabetics to respond to lipolytic and ketogenic hormones has been suggested by others as the basis for the clinically observed resistance to ketoacidosis. The present data do not confirm any failure of the liver or adipose tissue to respond to glucagon, epinephrine or norepinephrine in these diabetics. The ketosis-resistant young diabetics have some endogenous insulin secretory capacity still preserved as evident from their basal and post-glucose free insulin levels and effects of anti-insulin serum on in vitro lipolysis by their adipose tissues. The available endogenous insulin though adequate in preventing excessive lipolysis and ketogenesis, appears insufficient to check hyperglycemia.

Lipoprotein lipase activity in adipose tissue and skeletal muscle of human diabetics during insulin deprivation and restoration.

Twelve insulin-dependent diabetic patients were deprived of insulin for 12 h, and thereafter given an 8-h i.v. infusion of insulin. Lipoprotein lipase (LPL) activity was determined from heparin eluates of adipose tissue and skeletal muscle before and after insulin infusion. In spite of development of marked hyperglycemia and hyperketonaemia during the insulin deprivation the LPL activity of the two tissues remained mostly within normal range. During the subsequent insulin administration the LPL activity of adipose tissue increased by 36% (p less than 0.05) whereas the skeletal muscle LPL remained unchanged. The result is compatible with the view that human adipose tissue LPL is more sensitive to insulin than the corresponding enzyme of muscle.

Lipoprotein lipase activity of adipose tissue and skeletal muscle in insulin-deficient human diabetes

We have previously shown that lipoprotein lipase (LPL) activity of tissues is an important determinant not only of plasma VLDL levels but also of HDL-cholesterol. Studies were designed to investigate whether the serum lipoprotein alterations in uncontrolled insulin-deficient diabetes can be accounted for by changes in LPL activity of tissues. The heparin-releasable LPL activity was determined from biopsy samples of adipose tissue and skeletal muscle in 16 patients with newly detected untreated insulin-deficient diabetes and in 16 age-, sex- and body weight-matched healthy control subjects. Repeat assays were carried out after the patients had been on insulin treatment for an average of two weeks and when the diabetes was well controlled. When untreated the patients had increased concentrations of triglycerides and cholesterol in whole serum and in VLDL and LDL while the HDL cholesterol level was lower than that of controls (p<0.01). The cholesterol/triglyceride ratio in each of the three lipoproteins was similar in patients and controls. While untreated the diabetic patients had significantly reduced mean LPL activity both in adipose tissue (average 34% of control mean, p<0.001) and in skeletal muscle (average 45% of control mean, p<0.05). In the whole group HDL-cholesterol was positively correlated with adipose tissue LPL activity (r=+0.58, p<0.001) while log serum total triglyceride and log VLDL-triglyceride showed significant negative correlations with LPL activity of both adipose tissue and skeletal muscle. After initiation of insulin treatment the LPL activity increased significantly (p<0.01) in both tissues but was still subnormal after 2 weeks. At the same time the VLDL and LDL concentrations had returned to normal while the HDL-cholesterol remained low. The results suggest that the increase of VLDL and LDL triglyceride and the decrease of HDL-cholesterol present in uncontrolled insulin-deficient diabetes are, at least partly, accounted for by decreased LPL activity of tissues. The restoration of tissue LPL and of serum HDL-cholesterol by insulin are relatively slow processes. The results are consistent with the hypothesis that HDL-cholesterol concentration is dependent on the efficiency of removal of triglyceride-rich lipoproteins from the circulation.

The fatty acid pattern of triglycerides in liver, adipose tissue and serum of diabetics with hyperlipoproteinemia before and during clofibrate treatment.

In 20 diabetic inpatients with type IIb, III, IV and V hyperlipoproteinemia (HPL) the triglyceride fatty acid pattern (TFAP) of serum, adipose tissue and liver biopsy specimens before and after one year of clofibrate treatment has been determined by gas-liquid chromatography. Compared to previous results which revealed a correlation between fat droplet size and the TFAP in liver parenchyma cells, remarkable changes were observed after long-term therapy. In adipose tissue, only linoleic acid increased significantly from 8.6 to 11.3%. In serum, myristic and palmitic acid decreased, whereas linoleic, eicosatetraenoic (arachidonic) and eicosapentaenoic acid rose significantly. In liver fat, palmitic acid decreased, whereas linoleic, eicosatrienoic, arachidonic and eicosapentaenoic acid significantly increased. After clofibrate therapy, the TFAP in diabetic subjects with HLP became similar to that of diabetics without HLP. The most pronounced changes were found in the liver, serum having an intermediate position between liver and adipose tissue. The pathophysiological relevance in view of possible relations to prostaglandins has been discussed.

Abnormalities in the adrenergic control and the rate of lipolysis in isolated human subcutaneous adipose tissue in diabetes mellitus

Subcutaneous adipose tissue was obtained from 9 patients with untreated diabetes mellitus and from 13 obese nondiabetics. After incubation with isoprenaline or noradrenaline, glycerol release and tissue cyclic AMP (cAMP) were determined. Basal glycerol release was twice as rapid from the diabetic adipose tissue. With isoprenaline, the cAMP concentration and the glycerol production was significantly higher in the diabetic adipose tissue. Noradrenaline did not increase glycerol production or cAMP concentration in the diabetic adipose tissue. Subcutaneous adipose tissue was also removed from the diabetics after antidiabetic treatment. Basal lipolysis was significantly reduced and noradrenaline significantly increased both glycerol release and cAMP production. With isoprenaline, cAMP production and glycerol release were significantly less after antidiabetic treatment than in the untreated state. The data provide evidence for increased alpha- as well as beta-adrenergic receptor sensitivity in human subcutaneous adipose tissue of untreated diabetic patients.