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Biomedical subjects

C Grunfeld

Publications and source records attributed to C Grunfeld.

At least 163 records · Page 9Linked to original sources
PubMed1988

Mechanisms by which tumor necrosis factor stimulates hepatic fatty acid synthesis in vivo.

We have previously shown that bolus intravenous administration of tumor necrosis factor (TNF) to normal rats results in a rapid (within 90 min) stimulation of hepatic fatty acid synthesis, which is sustained for 17 hr. We now demonstrate that TNF stimulates fatty acid synthesis by several mechanisms. Fatty acid synthetase and acetyl-CoA carboxylase (measured after maximal stimulation by citrate) were not higher in livers from animals that had been treated with TNF 90 min before study compared to controls. In contrast, 16 hr after treatment with TNF, fatty acid synthetase was slightly elevated (35%) while acetyl-CoA carboxylase was increased by 58%. To explain the early rise in the hepatic synthesis of fatty acids, we examined the regulation of acetyl-CoA carboxylase. The acute increase in fatty acid synthesis was not due to activation of acetyl-CoA carboxylase by change in its phosphorylation state (as calculated by the ratio of activity in the absence and presence of 2 mM citrate). However, hepatic levels of citrate, an allosteric activator of acetyl-CoA carboxylase, were significantly elevated (51%) within 90 min of TNF treatment. TNF also induces an acute increase (within 90 min) in the plasma levels of free fatty acids. However, hepatic levels of fatty acyl-CoA, which can inhibit acetyl-CoA carboxylase, did not rise 90 min following TNF treatment and were 35% lower than in control livers by 16 hr after TNF. These data suggest that TNF acutely regulates hepatic fatty acid synthesis in vivo by raising hepatic levels of citrate.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetyl-CoA Carboxylase↗
PubMed1988

Aesthesiometry: quantification of cutaneous pressure sensation in diabetic peripheral neuropathy.

The Semmes-Weinstein pressure aesthesiometer, which measures cutaneous pressure sensation, was used for quantifying sensory loss in diabetic peripheral neuropathy. Eighty subjects comprising four groups were tested: nondiabetic controls (Group C); non-neuropathic, diabetic controls (Group DC); diabetic subjects with neuropathy and without a history of pedal ulcerations (Group DN); and, diabetic subjects with a history of or active pedal ulceration (Group DU). Cutaneous pressure sensation of 10 dorsal and plantar sites on the foot were tested, using a method of interval comparison modeled after the two-alternative forced choice algorithm. The sensitivity threshold level was defined as the lightest probe in which the subject accurately chose the correct interval in at least 2 out of 3 trials. The mean sensitivity threshold level for Group DC was not significantly increased (p greater than .05) compared to Group C. In contrast, patients with neuropathy (Group DN or DU) showed a significantly higher mean sensitivity threshold (p less than .001) than either Group C or DC. In addition, this technique demonstrated that patients in Group DU had a mean sensitivity threshold that was statistically higher (p less than .001) than Group DN, although both groups of patients had symptomatic neuropathy. This study provides a direct demonstration that decreased sensation of pressure occurs in the feet of diabetic patients with a history of ulceration. The best discrimination between groups is obtained by requiring that three of the six plantar forefoot sites have a sensitivity threshold level of greater than 5.07 log (0.1 mg) force as the risk discriminator level. Semmes-Weinstein aesthesiometry should now be tested in a prospective study to demonstrate its effectiveness in determining those patients at great risk of developing foot ulcers.

Adult↗
PubMed1987

Tumor necrosis factor-alpha stimulates hepatic lipogenesis in the rat in vivo.

The hyperlipidemia accompanying infection has been attributed to production of tumor necrosis factor. This cytokine inhibits adipose tissue lipoprotein lipase, which could decrease clearance of lipoproteins. Infections also increase hepatic lipogenesis. We now have demonstrated that tumor necrosis factor-alpha stimulates lipid synthesis in vivo. 2 h after administration of tumor necrosis factor (25 micrograms/200 g), plasma triglycerides increase 2.2-fold and remain elevated for 17 h. Plasma cholesterol also increases, but this effect appears after 7 h. Tumor necrosis factor rapidly stimulates incorporation of tritiated water into fatty acids in the liver (1-2 h), which persists for 17 h. Also, tumor necrosis factor stimulates hepatic sterol synthesis. Of note, tumor necrosis factor treatment does not stimulate lipid synthesis in other tissues, including adipose tissue. Labeled fatty acids rapidly increase in the plasma, raising the possibility that stimulation of hepatic lipogenesis by tumor necrosis factor contributes to the hyperlipidemia of infection.

Animals↗
PubMed1987

Identification of the intact insulin receptor using a sequence-specific antibody directed against the C-terminus of the beta-subunit.

An antibody was raised against a synthetic peptide corresponding to the carboxyl-terminal amino acids of the human insulin receptor (Anti-R beta C). Immunoprecipitation of the human insulin receptor and immunoblotting to the beta-subunit by Anti-R beta C could be inhibited by competition with the corresponding peptide. However, even at saturating concentrations, anti-R beta C could not completely immunoprecipitate or immunodeplete insulin receptors compared to a human autoantibody (anti-R B2). Using receptor labeled directly by 125I, evidence of multiple forms of the beta-subunit was found. When the receptor could be immunoprecipitated by anti-R beta C, the beta-subunit migrated with an apparent mol wt (MW) of 96,000 (at or above the phosphorylase b MW marker). However, in preparations where anti-R beta C was not able to immunoprecipitate the insulin receptor, the beta-subunit migrated at a significantly lower MW of 91,000 (below phosphorylase b), as detected by immunoprecipitation with Anti-R B2. Intermediate forms could also be detected. Phosphorylation of partially purified insulin receptor did not affect is ability to be immunoprecipitated by anti-R beta C, although insulin-stimulated phosphorylation increased the apparent MW of the beta-subunit. However, insulin receptor that was phosphorylated in solubilized extracts of whole cells had a beta-subunit that migrated at lower MW and was not immunoprecipitated by anti-R beta C. One possible explanation for this is that the beta-subunit may be degraded during preparation. When the MW of insulin receptor that has been purified to homogeneity from human placenta is compared to our data, it is clear that many of these insulin receptor preparations contain lower MW beta-subunits. These results must be taken into account when the sites of phosphorylation and kinase activity of purified insulin receptor preparations are studied.

Amino Acid Sequence↗
PubMed1987

Sonography of the hand and foot in foreign body detection.

To evaluate the possibility that sonography might be effective in the clinical detection of foreign bodies in the soft tissues, we used high-resolution sonography to study 10 patients with suspected foreign bodies in the hand and foot. Using ultrasound, we detected foreign bodies (glass, metal wire) in the sole of the foot of two patients and glass in the hand of another. Seven patients were proved to be free of foreign bodies. In an experimental model to ascertain which types of foreign bodies could be detected by ultrasound, wood, glass, and metallic foreign bodies 2.5 cm in length that had been inserted into the flesh of a chicken breast were immediately identified by high-resolution sonography. Ultrasound also pinpointed the surface beneath which the foreign bodies lay and localized all precisely as to depth from the surface. While detection of a foreign body is important, precise localization is crucial to avoid miscalculation of surgery leading to increased tissue damage, blood loss, and an increased risk of complications. This initial study suggests that high-resolution sonography has applicability in both the detection and the precise localization of foreign bodies in the soft tissues, but the sensitivity and specificity of the procedure remains to be determined.

Adult↗
PubMed1986

A trial of amitriptyline and fluphenazine in the treatment of painful diabetic neuropathy.

We conducted a double-blind, placebo-controlled, crossover study of the effectiveness of amitriptyline and fluphenazine in alleviating the pain of diabetic peripheral neuropathy in six diabetic patients. Pain was evaluated by the patients with a graphic rating scale. A placebo response was found, but no additional effect of amitriptyline and fluphenazine was seen. Although the statistical power of this study was low, these data, when combined with a reevaluation of previous trials of amitriptyline and fluphenazine in the treatment of painful diabetic neuropathy, indicate that there is no justification for the use of these agents in the treatment of painful neuropathy outside of large, controlled clinical trials. Depression as a possible cause of this condition should not go unnoted or untreated.

Adult↗
PubMed1986

Glucocorticoid-induced insulin resistance in vitro: inhibition of insulin-stimulated methylaminoisobutyric acid uptake.

We have previously developed an in vitro model for the induction of insulin resistance by glucocorticoids using 3T3-L1 fat cells (Grunfeld, Baird, Van Obberghen and Kahn 1981). In this model, glucocorticoid treatment was shown to decrease insulin binding and inhibit the acute stimulation of deoxyglucose uptake by insulin. We now extend the findings in this model to examine insulin stimulated methylaminoisobutyric acid (MAIB) uptake, an event whose expression requires m-RNA and protein synthesis and takes many hours. As previously seen with insulin stimulation of deoxyglucose uptake, one day of exposure to dexamethasone had little effect on insulin stimulation of MAIB uptake. Significant inhibition of insulin-stimulated MAIB uptake was seen after 2 days of exposure, and 3 days were required for the maximum effect of the glucocorticoid. The half-maximal concentration of dexamethasone required for inhibition was 1.6 nM. Exposure to dexamethasone produced a 57% decrease in the maximal response to insulin and a small but consistant shift in the sensitivity to insulin. As seen with the acute effects of insulin, the major locus of glucocorticoid action in inhibiting insulin stimulated MAIB uptake is also after the binding of insulin to its receptor. These data indicate that the inhibitory effects of glucocorticoids on insulin action in fat cells extend to those effects of insulin which require gene expression and are not merely limited to short-term metabolic actions of insulin.

Adipose Tissue↗
PubMed1986

Interferons and tumor necrosis factors have similar catabolic effects on 3T3 L1 cells.

The effect of a variety of cytokines on lipid metabolism in 3T3 L1 mouse fibroblasts and adipocytes was studied. Uptake of [3H]acetate by adipocytes and heparin-releasable lipoprotein lipase activity was inhibited after treatments of the cells with picomolar concentrations of recombinant human tumor necrosis factor alpha (rHuTNF-alpha), human tumor necrosis factor beta (rHuTNF-beta, also called lymphotoxin), murine interferon-gamma (rMuIFN-gamma), and a human hybrid interferon-alpha [rHuIFN-alpha 2/alpha 1 (Bgl II)]. Recombinant human interferon-gamma (rHuIFN-gamma), natural human colony-stimulating factor (HuCSF), and human interleukin 2 (HuIL-2) had no effect. Similar though less-marked suppression of [3H]acetate uptake by cytokines was seen in 3T3 L1 fibroblasts. Cytokines inhibited the incorporation of [3H]acetate into both membrane and storage lipids in the adipocytes. In addition to blocking lipid uptake and synthesis, rHuTNF-alpha and -beta, and rMuIFN-gamma stimulated the release of free fatty acid into the medium from adipocytes. Binding studies suggest that rHuTNF-alpha and rHuTNF-beta compete for the same cell-surface receptor on 3T3 L1 adipocytes, while rMuIFN-gamma binds to a separate receptor. The binding of rTNF-alpha to both adipocytes and fibroblasts can be significantly enhanced by preexposure of the cells to rMuIFN-gamma. There appear to be both high- and low-affinity receptors for rHuTNF-alpha on adipocytes, whereas fibroblasts exhibit a single class of high-affinity receptors. These results suggest that a variety of structurally distinct cytokines possess lipid mobilization activity, which may be of critical importance to the host in defense against infection or malignancy.

Acetates↗
PubMed1986

Differential sensitivity of two functions of the insulin receptor to the associated proteolysis: kinase action and hormone binding.

Since we observed that after purification the receptor kinase activity is rapidly lost under conditions where insulin binding function seems to be preserved, we have studied the cause(s) of receptor kinase inactivation. Highly purified placental insulin receptor preparations were analyzed by NaDodSO4/PAGE followed by silver staining or immunostaining using domain-specific antibodies raised against synthetic peptides corresponding to the amino acid sequences of the beta subunit. These studies revealed the intact 90-kDa beta subunit is degraded first to an 88-kDa form and then to a 50-kDa beta 1-subunit form by proteolysis even after purification when stored at 4 degrees C. The 88-kDa beta subunit, which lacks the carboxyl-terminal approximately equal to 2-kDa portion exhibits almost no autophosphorylation activity, nor does insulin stimulate autophosphorylation. The loss of kinase activity as measured by phosphorylation of the src-related peptide is correlated with the loss of the intact 90-kDa beta subunit. Degradation of the beta subunit to the 50-kDa form seems to be facilitated by the removal of the approximately equal to 2-kDa peptide. Present studies thus suggest that only the intact form of the beta subunit has full kinase activity in an insulin-dependent manner and that other forms, such as the 88-kDa beta subunit show little kinase activity. The inactivation appears to arise from a conformational change of the 90-kDa form, which makes it susceptible to proteolysis at the carboxyl-terminal end. These results imply that the carboxyl-terminal of the beta subunit is important for the manifestation of the tyrosine kinase activity of the insulin receptor.

Amino Acid Sequence↗
PubMed1986

Sonography of the sole of the foot. Evidence for loss of foot pad thickness in diabetes and its relationship to ulceration of the foot.

The hypothesis that loss of tissue mass in the foot contributes to foot ulceration in diabetics has never been quantitated. We developed normal criteria for the thickness of the sole of the foot at the heel, and the five metatarsal heads of both feet, using high-resolution ultrasound (10 MHz). We studied 24 normal patients ranging in weight from 125 to 250 lbs. We examined the soles of the feet of 38 diabetics without foot ulcers and 11 diabetics with foot ulcers or a history of foot ulcers who were in the same weight range as the normals. Of statistical significance, the heel thickness in controls was greater than that of the diabetics, which in turn was greater than that of the diabetics with foot ulcers. The thickness of the sole over the first and second metatarsals was also greater in the controls compared with diabetics. We conclude that high-resolution ultrasound is an effective determinant of the thickness of the sole of the foot and that diabetics have variations from the norm in the heel and at the first and second metatarsal heads.

Adipose Tissue↗
PubMed1985

Urea treatment allows dithiothreitol to release the binding subunit of the insulin receptor from the cell membrane: implications for the structural organization of the insulin receptor.

The sequence of the human insulin receptor has only one identifiable transmembrane region which is located in the beta subunit. The structure predicts that the alpha subunit, which binds insulin, is attached to the cell only by disulfide bonds to the beta subunit. However, treatment of membranes with dithiothreitol is ineffective at releasing the alpha subunit. If the receptor structure is unfolded with urea, dithiothreitol is able to release the alpha subunit. These data provided confirmatory evidence that the alpha subunit is not a transmembrane protein.

Cell Line↗
PubMed1985

Characterization of adrenocorticotropin receptors that appear when 3T3-L1 cells differentiate into adipocytes.

The binding of an 125I-labeled analog of ACTH, [125I]Tyr23,Phe2,Nle4-ACTH-(1-38), to differentiated 3T3-L1 fat cells was characterized. Time-dependent binding, which was inhibited by saturating concentrations of unlabeled ACTH (0.44 microM), could be demonstrated in the differentiated cells. Using 0.4 nM [125I]ACTH analog and increasing concentrations of ACTH, the half-maximal concentration for inhibition by ACTH was 4.3 nM. Scatchard analysis demonstrated a single class of ACTH binding. There were approximately 3500 binding sites/cell. The binding of [125I]ACTH analog was specific in that it could be displaced by ACTH, ACTH-(1-19), ACTH-(1-17), and N-acetyl-Ser1-ACTH, but not by high concentrations of insulin, beta-endorphin, or polylysine. There was an excellent correlation between the ability of ACTH and its analogs to inhibit [125I]ACTH analog binding and the ability of ACTH and its analogs to stimulate cAMP production. In contrast, no saturable binding could be demonstrated when undifferentiated 3T3-L1 fibroblasts, which are not responsive to ACTH, were studied. Thus, differentiation of 3T3-L1 cells into the adipocyte form is accompanied by the appearance of receptors for ACTH. These receptors allow the adipocytes to respond to ACTH.

Adipose Tissue↗
PubMed1985

Autoantibodies against the insulin receptor. Dissociation of the acute effects of the antibodies from the desensitization seen with prolonged exposure.

The effect of antibodies against the insulin receptor (anti-R) found in a patient with the type B syndrome of insulin resistance and acanthosis nigricans was characterized using 3T3-L1 cultured fat cells. Anti-R acutely mimicked the action of insulin by stimulating deoxyglucose uptake. With more prolonged exposure, this insulinomimetic effect decayed, glucose metabolism returned to basal levels, and the cells became severely resistant to the actions of insulin. As seen with anti-R from a previous patient, desensitization consisted of both a dramatic decrease in the maximal responsiveness of the cells to insulin and a shift in the dose-response curve for insulin-stimulated glucose oxidation. The acute and chronic effects of anti-R were then compared. The concentration of anti-R required to half-maximally inhibit insulin binding averaged more than twice that required for half-maximal stimulation of deoxyglucose uptake, consistent with the amount of spare receptors in 3T3-L1 cells. After prolonged exposure, the insulinomimetic activity was completely lost at all concentrations of anti-R, even at those that did not completely induce insulin resistance. Thus, loss of the insulinomimetic activity of anti-R is necessary, but not sufficient, to cause desensitization. Less anti-R was required to desensitize cells to insulin than would have been predicted on the basis of the acute inhibition of binding and the number of spare receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Heel pad thickness: determination by high-resolution ultrasonography.

Heel pad thickness classically is increased in acromegaly and can also be noted in long-term Dilantin therapy. A high-resolution 10-MHz dedicated superficial small parts real-time scanner was used to evaluate heel pad thickness without the use of radiation and without the magnification inherent in the standard procedure, a lateral radiograph of the foot. Fifty-four patients were studied, and it was determined in 10 controls that heel pad thickness averaged 16.6 mm. In 38 diabetics without ulcers of the feet, the heel pad was 17.8 mm. A single treated acromegalic had a heel pad thickness of 21 mm. Ultrasonography offers an effective alternative to radiography in the measurement of heel pad thickness.

Acromegaly↗
PubMed1984

Nicotinamide and other inhibitors of ADP-ribosylation block deoxyglucose uptake in cultured cells.

Nicotinamide was shown to inhibit deoxyglucose uptake in three diverse differentiated cell lines. In 3T3-L1 fat cells, nicotinamide equally inhibited basal and insulin stimulated deoxyglucose uptake. Inhibition by nicotinamide was non-competitive. A variety of inhibitors of ADP-ribosylation blocked deoxyglucose uptake while some analogs with no activity against ADP-ribose synthetase also had little effect on deoxyglucose uptake. These findings should be taken into account when inhibitors of ADP-ribosylation are used with intact cells.

Adenosine Diphosphate Ribose↗
PubMed1984

Antibody against the insulin receptor causes disappearance of insulin receptors in 3T3-L1 cells: a possible explanation of antibody-induced insulin resistance.

The effect of a rabbit antibody induced against the rat insulin receptor (RAR) was tested using cultured 3T3-L1 fat cells. As previously seen with antibodies against the insulin receptor from patients with the type B syndrome of insulin resistance and acanthosis nigricans, RAR acutely mimicked the action of insulin by stimulating deoxyglucose uptake. After prolonged exposure of 3T3-L1 cells to RAR, insulinomimetic activity was lost and the cells became resistant to the action of insulin. This state of insulin resistance is similar to that seen with the human autoantibodies. However, unlike antibody from the patients, RAR did not acutely inhibit the binding of insulin to its receptor; rather, RAR increased the binding of insulin to its receptor by a mechanism consistent with an increase in the affinity of the receptor for insulin. With prolonged exposure to RAR there was a dramatic decrease in insulin-receptor binding on the treated 3T3-L1 fat cells. These results suggest that antibody against the insulin receptor induces insulin resistance by a mechanism that involves loss of cell-surface insulin receptors.

Animals↗
PubMed1983

Evidence for cAMP-independent inhibition of S-phase DNA synthesis by prostaglandins.

Two prostaglandins, prostaglandin E1 (PGE1) and prostaglandin B1 (PGB1), block S-phase DNA synthesis in synchronous cultured baby hamster kidney (BHK) cells. The prostaglandin inhibition of DNA synthesis does not appear to require elevated levels of cAMP. In BHK-21 cells that have been "desensitized" to prostaglandin stimulation of adenylate cyclase and, therefore, have control levels of cAMP, PGE1 retains its inhibitory effect on the incorporation of tritiated thymidine into DNA. When BHK cells are exposed to PGB1 (a prostaglandin that does not elicit a cAMP response), DNA synthesis is also blocked. In nonsynchronous cells exposed for 1 h to PGE and then incubated for 1 h with PGE removed, a rebound of DNA synthesis occurs, therefore providing evidence that a transient rise of cAMP in itself is not capable of causing a cascade of reactions that block the synthesis of DNA. In addition, the concentration of PGE required for inhibition of DNA synthesis is significantly less than that required for cAMP generation. Addition of 1 x 10(-8) M PGE to BHK cells can be shown to significantly inhibit DNA synthesis within 30 min, with half-maximal inhibition seen at 3 x 10(-7) M PGE. Cyclic AMP levels for controls were 4.9 +/- 0.2 and 4.6 +/- 0.1 for 1 x 10(-6) M PGE1. These findings suggest that the prostaglandins can act independently of cAMP at physiological concentrations; and, therefore, it is possible that prostaglandins have a physiological role in the control of cell growth during S-phase.

Alprostadil↗