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Biomedical subjects

M K Sinha

Publications and source records attributed to M K Sinha.

At least 19 recordsLinked to original sources
PubMed1996

Ultradian oscillations of leptin secretion in humans.

We have recently demonstrated the nocturnal increase in leptin secretion in humans. In the present study we have examined the pulsatile pattern of leptin secretion using two different experimental protocols. The first protocol utilized blood samples withdrawn at 30 minute intervals immediately after meals, at 1 hour intervals between meals, and at 2 hour intervals during the night from 4 lean, 11 obese, and 5 obese NIDDM subjects. Analysis of circulating leptin levels by ULTRA algorithmic program and using matched intra-assay coefficient of variations demonstrated 1 to 7 ultradian oscillations with a mean of 3.25 +/- 0.36 (SEM) pulses per 24 hour period (period: 10.0 +/- 1.5 hours; mean relative amplitude: 0.52 +/- 0.06, n = 20). Significant positive correlations were observed for changes in absolute amplitude with body mass index (p < 0.025) and fasting leptin levels (< 0.0001). In the second series of experiments utilizing 15 minute blood sampling from 10 overnight fasted obese subjects (BMI 35.9 +/- 2.0 kg/m2), ultradian oscillations for leptin were more frequent, i.e., 2 to 7 oscillations (4.20 +/- 0.59), over a 12 hour duration (period: 3.44 +/- 0.49; mean relative amplitude: 0.28 +/- 0.03). The number of oscillations over a 12 hour period correlated significantly with BMI (p < 0.001), fasting leptin levels (p < 0.01), and absolute amplitude (p < 0.005) in a 15 minute sampling protocol. In summary, similar to other hormones, ultradian oscillations of leptin are observed in humans, although the physiological significance in relation to obesity or feeding behavior is not yet understood.

Blood Glucose↗
PubMed1996

Evidence of free and bound leptin in human circulation. Studies in lean and obese subjects and during short-term fasting.

Little is known about leptin's interaction with other circulating proteins which could be important for its biological effects. Sephadex G-100 gel filtration elution profiles of 125I-leptin-serum complex demonstrated 125I-leptin eluting in significant proportion associated with macromolecules. The 125I-leptin binding to circulating macromolecules was specific, reversible, and displaceable with unlabeled leptin (ED50: 0.73 +/- 0.09 nM, mean +/- SEM, n = 3). Several putative leptin binding proteins were detected by leptin-affinity chromatography of which either 80- or 100-kD proteins could be the soluble leptin receptor as approximately 10% of the bound 125I-leptin was immunoprecipitable with leptin receptor antibodies. Significantly higher (P < 0.001) proportions of total leptin circulate in the bound form in lean (46.5 +/- 6.6%) compared with obese (21.4 +/- 3.4%) subjects. In lean subjects with 21% or less body fat, 60-98% of the total leptin was in the bound form. Short-term fasting significantly decreased basal leptin levels in three lean (P < 0.0005) and three obese (P < 0.005) subjects while refeeding restored it to basal levels. The effects of fasting on free leptin levels were more pronounced in lean subjects (basal vs. 24-h fasting: 19.6 +/- 1.9 vs. 1.3 +/- 0.4 ng/ml) compared with those in obese subjects (28.3 +/- 9.8 vs. 14.7 +/- 5.3). No significant (P > 0.05) decrease was observed in bound leptin in either group. These studies suggest that in obese individuals the majority of leptin circulates in free form, presumably bioactive protein, and thus obese subjects are resistant to free leptin. In lean subjects with relatively low adipose tissue, the majority of circulating leptin is in the bound form and thus may not be available to brain receptors for its inhibitory effects on food intake both under normal and food deprivation states.

Carrier Proteins↗
PubMed1996

Decreased cerebrospinal-fluid/serum leptin ratio in obesity: a possible mechanism for leptin resistance.

BACKGROUND: A receptor for leptin has been cloned from the choroid plexus, the site of cerebrospinal-fluid (CSF) production and the location of the blood/cerebrospinal-fluid barrier. Thus, this receptor might serve as a transporter for leptin. We have studied leptin concentrations in serum and (CSF). METHODS AND FINDINGS: We demonstrated by radioimmunoassay and western blot the presence of leptin in human CSF. We then measured leptin in CSF and serum in 31 individuals with a wide range of bodyweight. Mean serum leptin was 318% higher in 8 obese (40.2 [SE 8.6] ng/mL) than in 23 lean individuals (9.6 [1.5] ng/mL, p < 0.0005). However, the CSF leptin concentration in obese individuals (0.337 [0.04] ng/mL) was only 30% higher than in lean people (0.259 [0.26] ng/mL, p < 0.1). Consequently, the leptin CSF/serum ratio in lean individuals (0.047 [0.010]) was 4.3-fold higher than that in obese individuals (0.011 [0.002], p < 0.05). The relation between CSF leptin and serum leptin was best described by a logarithmic function (r = 0 x 52, p < 0.01). INTERPRETATION: Our data suggest that leptin enters the brain by a saturable transport system. The capacity of leptin transport is lower in obese individuals, and may provide a mechanism for leptin resistance.

Biological Transport↗
PubMed1996

Nocturnal rise of leptin in lean, obese, and non-insulin-dependent diabetes mellitus subjects.

We studied 24-h profiles of circulating leptin levels using a sensitive and specific RIA in lean controls and obese subjects with or without non-insulin-dependent diabetes mellitus (NIDDM) during normal routine activity. Serum leptin levels were significantly higher in obese (41.7 +/- 9.0 ng/ml; n = 11) and obese NIDDM (30.8 +/- 6.7; n = 9) subjects compared with those in lean controls (12.0 +/- 4.4, n = 6). In all the three groups, serum leptin levels were highest between midnight and early morning hours and lowest around noon to midafternoon. The nocturnal rise in leptin levels was significant when data were analyzed by ANOVA (lean: F = 3.17, P < 0.0001, n = 4; obese: F = 2.02, P < 0.005, n = 11; and obese NIDDM: F = 4.9, P < 0.0001, n = 5). The average circadian amplitude between acrophase and nadir was 75.6% in lean, 51.7%, in obese and 60.7% in obese NIDDM groups, respectively. No significant correlations (P > 0.05) were observed between circulating levels of leptin and either insulin or glucose levels in any of the 20 subjects studied for 24-h profiles. The nocturnal rise in leptin observed in the present study resembles those reported for prolactin, thyroid-stimulating hormone, and free fatty acids. We speculate that the nocturnal rise in leptin could have an effect in suppressing appetite during the night while sleeping.

Adult↗
PubMed1996

Serum immunoreactive-leptin concentrations in normal-weight and obese humans.

BACKGROUND: 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 physiologic actions of leptin in humans. METHODS: Using a newly developed radioimmunoassay, wer measured serum concentrations of leptin in 136 normal-weight subjects and 139 obese subjects (body-mass index, > or = 27.3 for men and > or = 27.8 for women; the body-mass index was defined as the weight in kilograms divided by the square of the height in meters). The measurements were repeated in seven obese subjects after weight loss and during maintenance of the lower weight. The ob messenger RNA (mRNA) content of adipocytes was determined in 27 normal-weight and 27 obese subjects. RESULTS: The mean (+/- SD) serum leptin concentrations were 31.3 +/- 24.1 ng per milliliter in the obese subjects and 7.5 +/- 9.3 ng per milliliter in the normal-weight subjects (P < 0.001). There was a strong positive correlation between serum leptin concentrations and the percentage of body fat (r = 0.85, P < 0.001). The ob mRNA content of adipocytes was about twice as high in the obese subjects as in the normal-weight subjects (P < 0.001) and was correlated with the percentage of body fat (r = 0.68, P < 0.001) in the 54 subjects in whom it was measured. In the seven obese subjects studied after weight loss, both serum leptin concentrations and ob mRNA content of adipocytes declined, but these measures increased again during the maintenance of the lower weight. CONCLUSIONS: Serum leptin concentrations are correlated with the percentage of body fat, suggesting that most obese persons are insensitive to endogenous leptin production.

Adipocytes↗
PubMed1996

Paracrine stimulation of preadipocyte-enriched cell cultures by mature adipocytes.

We developed a double-chamber system in which to examine the effects of mature adipocytes on the growth and differentiation of preadipocytes and other cells in the adipose tissue. In the present study we found that mature adipocytes from both lean and obese subjects release a factor that stimulates the growth of preadipocyte-enriched and dedifferentiated adipocyte-enriched cell cultures. This growth stimulation was dependent on both time of exposure to mature cells and the number of mature cells in the coculture. Proliferation of the preadipocyte-enriched (n = 4) and dedifferentiated adipocyte-enriched cultures (n = 5) in the presence of mature adipocytes from obese subjects [body mass index (BMI) > 35] was 4.1- and 2.9-fold more (P < 0.05) than that in the presence of adipocytes from lean subjects (BMI < or = 25). There was no difference in the growth of cultures enriched in preadipocytes or dedifferentiated adipocytes from lean or obese subjects in the absence of mature adipocytes. These observations demonstrate that mature adipocytes from obese patients stimulate the growth of preadipocyte-enriched cultures to a greater extent than those from lean individuals.

Adipocytes↗
PubMed1994

High dose intravenous, but not low dose subcutaneous, insulin-like growth factor-I therapy induces sustained insulin sensitivity in severely resistant type I diabetes mellitus.

We have previously demonstrated weekly iv insulin-like growth factor-I (IGF-I; 500 micrograms/kg) bolus therapy to be effective in inducing sustained insulin sensitivity in a patient with type I diabetes mellitus and massive insulin resistance. The present study was undertaken to determine the efficacy of daily sc IGF-I in the treatment of two severely insulin-resistant type I diabetic patients (requiring in excess of 3500 U insulin/day) compared to weekly iv IGF-I therapy. Prolonged insulin sensitivity was achieved in both patients after weekly 500 micrograms/kg iv bolus infusions of IGF-I, with sc insulin requirements falling to approximately 1 U/kg.day. Smaller iv doses (250 micrograms/kg) of IGF-I were ineffective in acutely lowering serum glucose or inducing sustained insulin sensitivity. However, even this smaller IGF-I dose resulted in acute symptomatic hypophosphatemia, which could be prevented by coadministration of potassium phosphate. With sc administered IGF-I (up to 10 mg twice daily), insulin appeared to control patient glucose concentrations, but severe insulin resistance returned within 72 h of discontinuing IGF-I therapy. IGF-I dosing was decreased to the lowest concentration that maintained euglycemia (7.5 mg in the morning and 2.5 mg in the evening). However, severe arthropathy in both patients and neurological symptoms including multiple cranial nerve palsies in one patient were associated with chronic therapy. We conclude that both iv and sc administered IGF-I can precipitate acute symptomatic hypophosphatemia. Chronic low dose sc therapy may be associated with severe neuropathy and arthropathy, and does not induce the sustained insulin sensitivity associated with high dose intermittent bolus IGF-I therapy.

Adipocytes↗
PubMed1992

Surgical treatment of obesity and its effect on diabetes: 10-y follow-up.

Since 1980 we have performed the identical Greenville gastric bypass (GGB) procedure on 479 morbidly obese patients with an acceptable morbidity and a mortality rate of 1.2%. The weight loss in the series was well maintained over the follow-up period of 10 y. The GGB can control non-insulin-dependent diabetes mellitus (NIDDM) in most patients. The group of 479 patients included 101 (21%) with NIDDM and another 62 (13%) who were glucose impaired. Of these 163 individuals, 141 reverted to normal and only 22 (5%) remained with inadequate control of their carbohydrate metabolism. Those patients who were older or whose diabetes was of longer duration were less likely to revert to normal values. The gastric bypass operation is an effective approach for the treatment of morbid obesity. Along with its control of weight, the operation also controls the hyperglycemia, hyperinsulinemia, and insulin resistance of the majority of patients with either glucose impairment or frank NIDDM.

Adult↗
PubMed1992

Is type II diabetes mellitus (NIDDM) a surgical disease?

Since February 1, 1980, 515 morbidly obese patients have undergone the Greenville gastric bypass (GGB) operation. Of these, 212 (41.2%) were euglycemic, 288 (55.9%) were either diabetic or had glucose intolerance, and 15 (2.9%) were unable to complete the evaluation. After the operation, only 30 (5.8%) patients remained diabetic (and 20 of these improved), 457 (88.7%) became and have remained euglycemic, and inadequate data prevented classification of the other 28 (5.4%). The patients who failed to return to normal glucose values were older and their diabetes was of longer duration than those who did. The effect of the GGB was not only limited to the correction of abnormal glucose levels. The GGB also corrected the abnormal levels of fasting insulin and glycosylated hemoglobin in a cohort of 52 consecutive severely obese patients with non-insulin-dependent diabetes. The GGB effectively controls weight. If morbid obesity is defined as 100 pounds over ideal body weight, 89% of the patients are no longer "morbidly" obese within 2 years. In most patients, the control of the weight has been well maintained during the 11 years of follow-up; most of the upward creep in weight of 20.8% between 24 and 132 months was from the 49 (9.5%) patients who had staple line breakdowns between the large and small gastric pouches. Non-insulin-dependent diabetes, previously considered a chronic unrelenting disease, can be controlled in the severely obese by the gastric bypass. Whether the correction of glucose metabolism affects the complications of diabetes is unknown. Whether the gastric bypass should be considered for patients with advanced non-insulin-dependent diabetes but who are not severely obese deserves consideration. The GGB has an unacceptably high rate of staple line failure. Accordingly, the authors have recently changed their procedure to one that divides the stomach rather than partitions it with staples.

Adolescent↗
PubMed1991

Increased insulin responsiveness in isolated rat hepatocytes incubated with free fatty acid-poor albumin.

Freshly isolated rat hepatocytes incubated in a medium containing bovine serum albumin partially purified by charcoal treatment at pH 3 are three times more responsive to insulin with regard to alpha-aminoisobutyric acid uptake than those incubated in medium containing regular bovine serum albumin. This finding should facilitate future work in isolated hepatocytes, a cell system that for the most part has been considered relatively unresponsive to insulin.

Aminoisobutyric Acids↗
PubMed1991

Adipose tissue glucose transporters in NIDDM. Decreased levels of muscle/fat isoform.

We investigated the mechanism of peripheral insulin resistance in the adipose tissue of obese and non-insulin-dependent diabetes mellitus (NIDDM) patients at the level of the glucose-transport effector system. Freshly isolated adipocytes from obese nondiabetic and obese NIDDM subjects had decreased insulin sensitivity and responsiveness for glucose-transport stimulation compared with control subjects, with more pronounced changes associated with obese NIDDM patients. The relative abundance of muscle/fat glucose-transporter isoform in the three groups of subjects was determined by Western-blot analysis of detergent-soluble adipose tissue extracts with monoclonal antibody 1F8. Obesity per se had no effect on adipose tissue muscle/fat glucose-transporter isoform (3150 +/- 660 vs. 4495 +/- 410 counts/min [cpm]/mg protein). Furthermore, decreased levels of muscle/fat isoform in adipose tissue of NIDDM patients were also reflected in isolated adipocytes. Our results demonstrate that insulin resistance in isolated adipocytes of NIDDM patients could at least partly be due to a significant depletion of adipose tissue muscle/fat glucose-transporter isoform.

Adipose Tissue↗
PubMed1990

IGF-II receptors and IGF-II-stimulated glucose transport in human fat cells.

Insulin-like growth factor II (IGF-II) receptors have been described in rat but not in human adipocytes. In both species, IGF-II has been reported to stimulate glucose transport by interacting with the insulin receptor. In this study, we have unequivocally demonstrated the presence of IGF-II receptors in human adipocytes. 125I-labeled IGF-II specifically binds to intact adipocytes, membranes, and lectin-purified detergent solubilized extracts. Through the use of 0.5 mM disuccinimidyl suberate, 125I-IGF-II is cross-linked to a 260-kDa protein that is identified as the IGF-II receptor by displacement experiments with unlabeled IGF-II, IGF-I, and insulin and either by immunoprecipitation or by Western blot analysis with mannose 6-phosphate receptor antibodies. The concentrations of IGF-II required for half-maximal and maximal stimulation of glucose transport in human adipocytes are 35 and 100 times more than that of insulin. The possibility of IGF-II stimulating glucose transport by interacting predominantly with the insulin receptor is suggested by the following: 1) the concentration of IGF-II that inhibits half of insulin binding is only 20 times more than that of insulin; 2) the lack of an additive effect of IGF-II and insulin for maximal stimulation of glucose transport; 3) the ability of monoclonal insulin receptor antibodies to decrease glucose transport stimulated by submaximal concentrations of both IGF-II and insulin; and 4) the ability of IGF-II to stimulate insulin receptor autophosphorylation albeit at a reduced potency when compared with insulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1989

Glyburide but not ciglitazone enhances insulin action in the liver independent of insulin receptor kinase activation.

To test the hypothesis that sulfonylureas enhance insulin action by activating the insulin receptor tyrosine kinase, the effects of glyburide, a second generation sulfonylurea, and ciglitazone, a nonsulfonylurea hypoglycemic agent, were determined in primary cultures of rat hepatocytes on insulin action and insulin receptor structure and function. Twenty hours of preincubation with glyburide (1 microgram/mL) resulted in increased insulin (1 X 10(-7) mol/L) stimulation of [14C] acetate incorporation into lipids and [14C] alpha-aminoisobutyric acid uptake without any change in basal activity. Ciglitazone (1 microgram/mL) was without any effect. Glyburide's actions were mediated without altering the following: (1) 125I-insulin binding; (2) the electrophoretic mobility of the affinity labeled alpha-subunit or the autophosphorylated beta-subunit of the insulin receptor; and (3) the insulin-stimulated insulin receptor kinase activity using histone or the beta-subunit of the insulin receptor as phosphoacceptors. These data suggest that the action of sulfonylureas is distal to the insulin receptor tyrosine kinase. Ciglitazone in vitro is ineffective in the liver, which suggests the peripheral tissues as the possible site of action.

Animals↗
PubMed1989

Mechanism of IGF-I-stimulated glucose transport in human adipocytes. Demonstration of specific IGF-I receptors not involved in stimulation of glucose transport.

We demonstrate the presence of specific insulinlike growth factor I (IGF-I) receptors in human adipocytes. Competition studies with 125I-labeled IGF-I and unlabeled IGF-I, IGF-II, and insulin showed the specificity of 125I-IGF-I binding to the IGF-I receptors in adipocytes, membranes, and partially purified detergent-solubilized extracts. The monoclonal antibody to the IGF-I receptor (alpha-IR3) inhibits 125I-IGF-I binding and immunoprecipitates the IGF-I receptor. In addition, the alpha-subunit of IGF-I receptor is approximately 10,000 Mr larger than the alpha-subunit of insulin receptor, and IGF-I stimulates phosphorylation of the beta-subunit of the IGF-I receptor. IGF-I stimulates basal glucose transport in human adipocytes, but the concentrations of IGF-I required for half-maximal and maximal stimulation of glucose transport are 800- and 1000-fold greater than that of insulin. The possibility of IGF-I stimulating glucose transport by interacting predominantly with insulin receptors is suggested by data showing that 1) IGF-I competes with insulin-binding sites, 2) there is a lack of an additive effect with IGF-I and insulin in stimulating glucose transport, 3) alpha-IR3, which specifically inhibits IGF-I binding, does not inhibit IGF-I or insulin-stimulated glucose transport, 4) insulin-receptor antibody MA-10 inhibits IGF-I and insulin-stimulated glucose transport, and 5) IGF-I stimulates insulin-receptor autophosphorylation, although its effect is markedly decreased compared with insulin. In summary, human adipocytes possess specific IGF-I receptors. However, IGF-I stimulates glucose transport predominantly by interacting with the insulin receptor.

Adipose Tissue↗