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Biomedical subjects

J F Caro

Publications and source records attributed to J F Caro.

At least 55 records · Page 3Linked to original sources
PubMed1996

The hypothalamic leptin receptor in humans: identification of incidental sequence polymorphisms and absence of the db/db mouse and fa/fa rat mutations.

Leptin-receptor gene expression in hypothalamic tissue from lean and obese humans was examined. The full-length leptin receptor, that is believed to transmit the leptin signal, is expressed in human hypothalamus. There was no difference in the amount of leptin-receptor mRNA In seven lean (BMI 23.3 +/- 0.9 kg/m2) and eight obese (BMI 36.9 +/- 1.5) subjects as determined by reverse transcription-polymerase chain reaction. A sequence polymorphism (A-->G) was detected at position 668 of the leptin receptor cDNA. This second base substitution changed a glutamine to an arginine at position 223 of the leptin receptor protein. Of 15 subjects analyzed, 11 were heterozygous for this base change and 3 were homozygous. The occurrence [correction of occurance] of the polymorphic allele(s) did not correlate with BMI in the population studied. The mutation responsible for the defect in the leptin receptor in db/db mice was not detected in any obese human, nor was the fa/fa rat mutation. These results provide evidence that the leptin resistance observed in obese humans is not due to a defect in the leptin receptor.

Animals↗
PubMed1996

Effect of troglitazone on leptin production. Studies in vitro and in human subjects.

Leptin, the product of the ob gene, is a hormone secreted by adipocytes. Animals with mutations in the ob gene are obese and lose weight when given leptin, but little is known about the physiological role of leptin in humans. Obese subjects have higher concentrations of leptin than lean subjects, the strongest correlation being with percentage body fat. Thus, it appears that obese subjects are resistant to the effects of endogenously secreted leptin. We have also shown that insulin stimulates leptin production, chronically but not acutely, presumably through its trophic effect on adipocytes. Troglitazone is an insulin-sensitizing thiazolidinedione, which improves hepatic and skeletal muscle insulin resistance in NIDDM and obesity. This study was undertaken to investigate the effects of troglitazone on leptin production in vitro and in vivo. In the presence and absence of 100 nmol/l insulin and 10 umol/l troglitazone, 72-h primary cultures of isolated abdominal adipocytes were studied. Insulin led to an almost twofold increase in leptin in vitro, and this increase was completely abolished by coincubation with troglitazone. Incubation with troglitazone alone led to a 40% decrease in leptin production. In obese patients administered troglitazone 200 mg twice daily for 12 weeks, there was no significant change in fasting plasma leptin concentrations, despite a 40-50% reduction in fasting and postmeal plasma insulin concentrations. Troglitazone treatment led to a significant increase in insulin sensitivity, and there was a positive correlation between the change in insulin sensitivity and the change in plasma leptin concentration in these subjects. In conclusion, troglitazone treatment had no net effect on plasma leptin concentrations, possibly because of improvement in insulin sensitivity and reduction in plasma insulin concentrations.

Adipocytes↗
PubMed1996

The ABCs of managing hyperthyroidism in the older patient.

Hyperthyroidism in the older patient often presents with nonspecific symptoms, such as apathy, weight loss, and atrial fibrillation. General screening is not cost-effective, with the exception of two populations: women over age 40 with one or more nonspecific complaints and patients being admitted to a specialized geriatric unit. The sensitive TSH test is an excellent screen; a low TSH should be confirmed by an actual or estimated high free thyroxine test (FT4). The RAIU can help narrow the differential diagnosis. Radioiodine is the preferred treatment for the older patient with Graves' disease, the most common form of thyrotoxicosis. Graves' must be differentiated from thyroiditis and toxic nodular goiters, as treatment regimens differ for each disorder.

Age Factors↗
PubMed1996

Serum leptin in children with obesity: relationship to gender and development.

BACKGROUND: The identification of the ob gene and its adipocyte-specific protein leptin has provided the first physiologic links to the regulatory system controlling body weight. In adults, elevations of serum leptin concentrations were closely correlated with the percentage of body fat. This study investigated whether leptin concentrations were elevated in obese children and the relationship between leptin concentrations and gender, pubertal stage, and race. METHODS: Seventy-seven children (44 girls and 33 boys), mean age, 11.3 years, with a body mass indices (BMIs) greater than 95% for age, race, and gender (mean BMI, 34.4) constituted the obese group. Thirty children (20 girls and 10 boys), mean age, 13.3 years, with BMIs less than 85% for age, race, and sex formed the control group. Radioimmunoassay for serum leptin was performed on a blood sample collected from each child after an overnight fast. RESULTS: The mean serum concentration of leptin in the obese group was 38.6 (SD, 21) ng/mL compared with 7.8 (SD, 6.5) ng/mL in the control group. Serum leptin concentrations were highly correlated with BMI (r = .88). Analysis of covariance revealed a main effect for Tanner stage and gender. CONCLUSIONS: As in adults, obese children have high concentrations of serum leptin, which were highly correlated with arm fat and BMI. Increased adipose tissue in children is associated directly with serum leptin concentration. Leptin concentrations were found to vary with Tanner stage independent of adiposity. Compared with boys, girls had increased leptin concentrations independent of adiposity. It was hypothesized that children manifest a relative "leptin resistance" to support increased growth and development of reproductive capacity.

Adipose Tissue↗
PubMed1995

Liver glucokinase: decreased activity in patients with type II diabetes.

Because of the demonstration of a genetic linkage between glucokinase and Type II diabetes, and the central role of glucokinase on glucose metabolism, we studied glucokinase activity in the liver of patients with and without Type II diabetes. Glucokinase activity was decreased by about 50% in obese subjects with diabetes (n = 12) compared with (p < 0.01) lean controls (n = 9) and (p < 0.05) obese controls (n = 10). There was no difference between lean and obese controls. Fifty percent of subjects with diabetes had lower liver glucokinase activity than the lowest value of the controls. These data further support the important role that glucokinase plays in the pathogenesis of Type II diabetes.

Adult↗
PubMed1995

Increased adipose tissue expression of tumor necrosis factor-alpha in human obesity and insulin resistance.

Obesity is frequently associated with insulin resistance and abnormal glucose homeostasis. Recent studies in animal models have indicated that TNF-alpha plays an important role in mediating the insulin resistance of obesity through its overexpression in fat tissue. However, the mechanisms linking obesity to insulin resistance and diabetes in humans remain largely unknown. In this study we examined the expression pattern of TNF-alpha mRNA in adipose tissues from 18 control and 19 obese premenopausal women by Northern blot analysis. TNF-alpha protein concentrations in plasma and in conditioned medium of explanted adipose tissue were measured by ELISA. Furthermore, the effects of weight reduction by dietary treatment of obesity on the adipose expression of TNF-alpha mRNA were also analyzed in nine premenopausal obese women, before and after a controlled weight-reduction program. These studies demonstrated that obese individuals express 2.5-fold more TNF-alpha mRNA in fat tissue relative to the lean controls (P < 0.001). Similar increases were also observed in adipose production of TNF-alpha protein but circulating TNF-alpha levels were extremely low or undetectable. A strong positive correlation was observed between TNF-alpha mRNA expression levels in fat tissue and the level of hyperinsulinemia (P < 0.001), an indirect measure of insulin resistance. Finally, body weight reduction in obese subjects which resulted in improved insulin sensitivity was also associated with a decrease in TNF-alpha mRNA expression (45%, P < 0.001) in fat tissue. These results suggest a role for the abnormal regulation of this cytokine in the pathogenesis of obesity-related insulin resistance.

Adipose Tissue↗
PubMed1995

Protein kinase C is increased in the liver of humans and rats with non-insulin-dependent diabetes mellitus: an alteration not due to hyperglycemia.

We tested the hypothesis that liver protein kinase C (PKC) is increased in non-insulin-dependent diabetes mellitus (NIDDM). To this end we examined the distribution of PKC isozymes in liver biopsies from obese individuals with and without NIDDM and in lean controls. PKC isozymes alpha, beta, epsilon and zeta were detected by immunoblotting in both the cytosol and membrane fractions. Isozymes gamma and delta were not detected. There was a significant increase in immunodetectable PKC-alpha (twofold), -epsilon (threefold), and -zeta (twofold) in the membrane fraction isolated from obese subjects with NIDDM compared with the lean controls. In obese subjects without NIDDM, the amount of membrane PKC isozymes was not different from the other two groups. We next sought an animal model where this observation could be studied further. The Zucker diabetic fatty rat offered such a model system. Immunodetectable membrane PKC-alpha, -beta, -epsilon, and -zeta were significantly increased when compared with both the lean and obese controls. The increase in immunodetectable PKC protein correlated with a 40% elevation in the activity of PKC at the membrane. Normalization of circulating glucose in the rat model by either insulin or phlorizin treatment did not result in a reduction in membrane PKC isozyme protein or kinase activity. Further, phlorizin treatment did not improve insulin receptor autophosphorylation nor did the treatment lower liver diacylglycerol. We conclude that liver PKC is increased in NIDDM, a change that is not secondary to hyperglycemia. It is possible that PKC-mediated phosphorylation of some component in the insulin signaling cascade contributes to the insulin resistance observed in NIDDM.

Adult↗
PubMed1995

Evidence against either a premature stop codon or the absence of obese gene mRNA in human obesity.

Obese (ob) gene expression in abdominal subcutaneous adipocytes from lean and obese humans was examined. The full coding region of the ob gene was isolated from a human adipocyte cDNA library. Translation of the insert confirmed the reported amino acid sequence. There was no difference in the sequence of an reverse transcription PCR product of the coding region from five lean and five obese subjects. The nonsense mutation in the ob mouse which results in the conversion of arginine 105 to a stop codon was not present in human obesity. In all 10 human cDNAs, arginine 105 was encoded by CGG, consequently two nucleotide substitutions would be required to result in a stop codon. To compare the amount of ob gene expression in lean and obese individuals, radiolabed primer was used in the PCR reaction with beta-actin as a control. There was 72% more ob gene expression (P < 0.01) in eight obese subjects (body mass index, BMI = 42.8 +/- 2.7) compared to eight lean controls (BMI = 22.4 +/- 0.8). Regression analysis indicated a positive correlation between BMI and the amount of ob message (P < 0.005). There was no difference in the amount of beta-actin expression in the two groups. These results provide evidence that ob gene expression is increased in human obesity; furthermore, the mutations present in the mouse ob gene were not detected in the human mRNA population.

Adult↗
PubMed1994

Stimulation of glucose uptake by insulin-like growth factor II in human muscle is not mediated by the insulin-like growth factor II/mannose 6-phosphate receptor.

Although the growth-promoting effects of insulin-like growth factor II (IGF-II) have been intensively studied, the acute actions of this hormone on glucose metabolism have been less well evaluated, especially in skeletal muscle of humans. We and other groups have shown that IGFs reduce glycaemic levels in humans and stimulate glucose uptake in rat muscle. The purpose of the present study was to evaluate the effect of IGF-II on glucose transport in muscle of normal and obese patients with and without non-insulin-dependent diabetes mellitus (NIDDM), as well as to identify the receptor responsible for this action. 2-Deoxyglucose transport was determined in vitro using a muscle-fibre strip preparation. IGF-II were investigated in biopsy material of rectus abdominus muscle taken from lean and obese patients and obese patients with NIDDM at the time of surgery. In the lean group, IGF-II (100 nM) stimulated glucose transport 2.1-fold, which was slightly less than stimulation by insulin (2.8-fold) at the same concentration. Binding of IGF-II was approx. 25% of that of insulin at 1 nM concentrations of both hormones. Obesity with or without NIDDM significantly reduced IGF-II-stimulated glucose uptake compared with the lean group. In order to explore which receptor mediated the IGF-II effect, we compared glucose uptake induced by IGF-II and two IGF-II analogues: [Leu27]IGF-II, with high affinity for the IGF-II/Man 6-P receptor but markedly reduced affinity for the IGF-I and insulin receptors, and [Arg54,Arg55]IGF-II was similar to that of IGF-II, whereas [Leu27]IGF-II had a very diminished effect. Results show that IGF-II is capable of stimulating muscle glucose uptake in lean but not in obese subjects and this effect seems not to be mediated via an IGF-II/Man 6-P receptor.

Adult↗
PubMed1994

Insulin-like growth factor-1 therapy in diabetes: physiologic basis, clinical benefits, and risks.

PURPOSE: To review the effects of insulin-like growth factor-1 (IGF-1) and to discuss the clinical benefits and risks of using it in patients with diabetes. DATA SOURCES: Recent publications identified through a MEDLINE search using relevant keywords. STUDY SELECTION: Selected studies on the metabolic effects and kinetic mechanisms of in vitro IGF-1 and existing literature on the effects of IGF-1 on glucose and lipid metabolism in vivo with special emphasis on data from humans. DATA SYNTHESIS: The substantial stimulatory effect of IGF-1 on glucose uptake suggests that, in selected clinical situations, the drug may be an alternative to standard treatment of diabetes. Metabolic control in patients with extreme insulin resistance is improved after using IGF-1. Moreover, patients with type II (non-insulin-dependent) diabetes who receive IGF-1 have improved glucose tolerance and decreased hyperinsulinemia and hypertriglyceridemia. The complications associated with long-term administration of IGF-1 are unknown but might include the progression of certain neoplasms and diabetic complications, such as nephropathy and retinopathy. CONCLUSIONS: Insulin-like growth factor-1 may be a useful adjunct for treatment of diabetes and may even be the drug of choice in some patients with extreme insulin resistance who have metabolic emergencies. However, further data are needed to evaluate the risks and benefits of IGF-1 use in diabetes and in other states associated with impaired insulin action.

Animals↗
PubMed1994

Guanine nucleotide binding regulatory proteins in liver from obese humans with and without type II diabetes: evidence for altered "cross-talk" between the insulin receptor and Gi-proteins.

A novel pathway for physiological "cross-talk" between the insulin receptor and the regulatory Gi-protein has been demonstrated. We tested the hypothesis that a coupling defect between Gi and the insulin receptor is present in the liver of obese patients with and without type II diabetes. Insulin 1 x 10(-9) M (approximately ED50) and 1 x 10(-7) M (Max) inhibited pertussis toxin-catalyzed ADP ribosylation of Gi in human liver plasma membranes from lean and obese nondiabetic patients. However, 1 x 10(-7) M insulin was without effect in membranes from patients with type II diabetes. This coupling defect was not intrinsic to Gi, since Mg2+ and GTP gamma S inhibited pertussis toxin-catalyzed ADP ribosylation in both diabetic and nondiabetic patients. Binding of insulin of the alpha-subunit and activation of the tyrosine kinase intrinsic to the beta-subunit of the insulin receptor are not responsible for the coupling defect. 125I insulin binding is the same in obese patients with or without diabetes. Tyrosine kinase of the insulin receptor is decreased in diabetes. However, a monoclonal antibody to the insulin receptor (MA-20) at equimolar concentrations with insulin equally inhibits pertussis toxin-catalyzed ADP ribosylation of Gi without activating tyrosine kinase or insulin receptor autophosphorylation. Immunodetection of G-proteins suggested that Gi3 alpha was normal in diabetes and Gi1-2 alpha was decreased by 40% in the diabetic group as compared to the obese nondiabetic group but was normal when compared to the lean non diabetic group. We conclude that the novel pathway of insulin signaling involving the regulatory Gi proteins via biochemical mechanisms not directly involving the tyrosine kinase of the insulin receptor is altered in obese type II diabetes and offers a new target for the search of the mechanism(s) of insulin resistance.

Adenosine Diphosphate Ribose↗
PubMed1994

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)

Adult↗
PubMed1994

Circulating insulin-like growth factor I concentrations in clinically severe obese patients with and without NIDDM in response to weight loss.

Earlier studies have demonstrated decreased levels of circulating Insulin-Like Growth Factor-I (IGF-I) in patients with NIDDM and IDDM (Yde 1969; Rieu and Binoux 1985), with a return to normal in those diabetics who achieve improved metabolic control (Rieu and Binoux 1985; Ameil, Sherwin, Hintz, Gertner, Press and Tamborlane 1984) following insulin therapy. One method of improving metabolic control in clinically severe obese NIDDM patients is the gastric bypass procedure (GBP). This study revealed a significant decrease in serum IGF-I concentrations in clinically severe obese patients with NIDDM (obese NIDDM) (105 ng/dl +/- 11; n = 29) as compared with clinically severe obese patients with normal glucose tolerances (obese control) (143 +/- 11; n = 21) and lean controls (177 +/- 14; n = 19) (p < 0.001). Following a GBP, IGF-I levels increased in the NIDDM group (142 ng/dl +/- 13.0; n = 20) to the extent that no significant difference was seen between postoperative NIDDM, obese controls, and lean controls. Postoperative IGF-I levels in the obese controls (151 +/- 14; n = 9) revealed no difference from preoperative levels. Postoperative obese NIDDM and obese control had a 28% and 29% decrease, respectively, in weight, with no difference between the groups in respect to Body Mass Indices. The NIDDM postoperative group revealed reductions in levels of HbA1C, insulin, and glucose concurrent with elevations in IGF-I when compared with controls. We conclude that improvement in glucose control led to the increase in IGF-I levels.

Adult↗
PubMed1994

Weight loss in severely obese subjects prevents the progression of impaired glucose tolerance to type II diabetes. A longitudinal interventional study.

OBJECTIVE: To determine if weight loss may prevent conversion of impaired glucose tolerance (IGT) to diabetes, because weight loss reduces insulin resistance. The prevalence of IGT in the U.S. population is estimated at 11.2%, more than twice that of diabetes. Furthermore, because an oral glucose tolerance test is needed for its detection, most of these patients are undiagnosed. Screening for IGT would be meaningful if progression to diabetes could be delayed or prevented. RESEARCH DESIGN AND METHODS: For an average of 5.8 years (range 2-10 years), 136 individuals with IGT and clinically severe obesity (> 45 kg excess body weight) were followed. The experimental group included 109 patients with IGT who underwent bariatric surgery for weight loss. The control group was made up of 27 subjects with IGT who did not have bariatric surgery. The criteria of the World Health Organization was used to detect IGT and diabetes in this population. The main outcome measure of this nonrandomized control trial is the incidence density, or number of events (development of diabetes) divided by the time of exposure to risk. RESULTS: Of the 27 subjects in the control group, 6 developed diabetes during an average of 4.8 +/- 2.5 years of postdiagnosis follow-up, yielding a rate of conversion to diabetes of 4.72 cases per 100 person-years. The 109 individuals of the experimental group were followed for an average of 6.2 +/- 2.5 years postbariatric surgery. Based on the 95% confidence interval of the comparison group, we would expect to find that between 22 and 36 subjects in the experimental group developed diabetes over the follow-up period. Only 1 of the 109 experimental-group patients developed diabetes, resulting in a conversion rate of the experimental group of only 0.15 cases per 100 person-years, which is significantly lower (P < 0.0001) than the control group. CONCLUSIONS: Weight loss in patients with clinically severe obesity prevents the progression of IGT to diabetes by > 30-fold.

Adult↗