Ghrelin induces adiposity in rodents

The discovery of the peptide hormone ghrelin, an endogenous ligand for the growth hormone secretagogue (GHS) receptor, yielded the surprising result that the principal site of ghrelin synthesis is the stomach and not the hypothalamus. Although ghrelin is likely to regulate pituitary growth hormone (GH) secretion along with GH-releasing hormone and somatostatin, GHS receptors have also been identified on hypothalamic neurons and in the brainstem. Apart from potential paracrine effects, ghrelin may thus offer an endocrine link between stomach, hypothalamus and pituitary, suggesting an involvement in regulation of energy balance. Here we show that peripheral daily administration of ghrelin caused weight gain by reducing fat utilization in mice and rats. Intracerebroventricular administration of ghrelin generated a dose-dependent increase in food intake and body weight. Rat serum ghrelin concentrations were increased by fasting and were reduced by re-feeding or oral glucose administration, but not by water ingestion. We propose that ghrelin, in addition to its role in regulating GH secretion, signals the hypothalamus when an increase in metabolic efficiency is necessary.

A preprandial rise in plasma ghrelin levels suggests a role in meal initiation in humans

The recently discovered orexigenic peptide ghrelin is produced primarily by the stomach and circulates in blood at levels that increase during prolonged fasting in rats. When administered to rodents at supraphysiological doses, ghrelin activates hypothalamic neuropeptide Y/agouti gene-related protein neurons and increases food intake and body weight. These findings suggest that ghrelin may participate in meal initiation. As a first step to investigate this hypothesis, we sought to determine whether circulating ghrelin levels are elevated before the consumption of individual meals in humans. Ghrelin, insulin, and leptin were measured by radioimmunoassay in plasma samples drawn 38 times throughout a 24-h period in 10 healthy subjects provided meals on a fixed schedule. Plasma ghrelin levels increased nearly twofold immediately before each meal and fell to trough levels within 1 h after eating, a pattern reciprocal to that of insulin. Intermeal ghrelin levels displayed a diurnal rhythm that was exactly in phase with that of leptin, with both hormones rising throughout the day to a zenith at 0100, then falling overnight to a nadir at 0900. Ghrelin levels sampled during the troughs before and after breakfast correlated strongly with 24-h integrated area under the curve values (r = 0.873 and 0.954, respectively), suggesting that these convenient, single measurements might serve as surrogates for 24-h profiles to estimate overall ghrelin levels. Circulating ghrelin also correlated positively with age (r = 0.701). The clear preprandial rise and postprandial fall in plasma ghrelin levels support the hypothesis that ghrelin plays a physiological role in meal initiation in humans.

Plasma ghrelin levels after diet-induced weight loss or gastric bypass surgery

BACKGROUND

Weight loss causes changes in appetite and energy expenditure that promote weight regain. Ghrelin is a hormone that increases food intake in rodents and humans. If circulating ghrelin participates in the adaptive response to weight loss, its levels should rise with dieting. Because ghrelin is produced primarily by the stomach, weight loss after gastric bypass surgery may be accompanied by impaired ghrelin secretion.

METHODS

We determined the 24-hour plasma ghrelin profiles, body composition, insulin levels, leptin levels, and insulin sensitivity in 13 obese subjects before and after a six-month dietary program for weight loss. The 24-hour ghrelin profiles were also determined in 5 subjects who had lost weight after gastric bypass and 10 normal-weight controls; 5 of the 13 obese subjects who participated in the dietary program were matched to the subjects in the gastric-bypass group and served as obese controls.

RESULTS

Plasma ghrelin levels rose sharply shortly before and fell shortly after every meal. A diet-induced weight loss of 17 percent of initial body weight was associated with a 24 percent increase in the area under the curve for the 24-hour ghrelin profile (P=0.006). In contrast, despite a 36 percent weight loss after gastric bypass, the area under the curve for the ghrelin profile in the gastric-bypass group was 77 percent lower than in normal-weight controls (P<0.001) and 72 percent lower than in matched obese controls (P=0.01). The normal, meal-related fluctuations and diurnal rhythm of the ghrelin level were absent after gastric bypass.

CONCLUSIONS

The increase in the plasma ghrelin level with diet-induced weight loss is consistent with the hypothesis that ghrelin has a role in the long-term regulation of body weight. Gastric bypass is associated with markedly suppressed ghrelin levels, possibly contributing to the weight-reducing effect of the procedure.

Circulating ghrelin levels are decreased in human obesity

Ghrelin is a novel endogenous natural ligand for the growth hormone (GH) secretagogue receptor that has recently been isolated from the rat stomach. Ghrelin administration stimulates GH secretion but also causes weight gain by increasing food intake and reducing fat utilization in rodents. To investigate the possible involvement of ghrelin in the pathogenesis of human obesity, we measured body composition (by dual X-ray absorption) as well as fasting plasma ghrelin concentrations (radioimmunoassay) in 15 Caucasians (8 men and 7 women, 31+/-9 years of age, 92+/-24 kg body wt, and 29+/-10% body fat, mean +/- SD) and 15 Pima Indians (8 men and 7 women, 33+/-5 years of age, 97+/-29 kg body wt, and 30+/-8% body fat). Fasting plasma ghrelin was negatively correlated with percent body fat (r = -0.45; P = 0.01), fasting insulin (r = -0.45; P = 0.01) and leptin (r = -0.38; P = 0.03) concentrations. Plasma ghrelin concentration was decreased in obese Caucasians as compared with lean Caucasians (P < 0.01). Also, fasting plasma ghrelin was lower in Pima Indians, a population with a very high prevalence of obesity, compared with Caucasians (87+/-28 vs. 129+/-34 fmol/ml; P < 0.01). This result did not change after adjustment for fasting plasma insulin concentration. There was no correlation between fasting plasma ghrelin and height. Prospective clinical studies are now needed to establish the role of ghrelin in the pathogenesis of human obesity.

Ghrelin enhances appetite and increases food intake in humans

Ghrelin is a recently identified endogenous ligand for the growth hormone secretagogue receptor. It is synthesized predominantly in the stomach and found in the circulation of healthy humans. Ghrelin has been shown to promote increased food intake, weight gain and adiposity in rodents. The effect of ghrelin on appetite and food intake in man has not been determined. We investigated the effects of intravenous ghrelin (5.0 pmol/kg/min) or saline infusion on appetite and food intake in a randomised double-blind cross-over study in nine healthy volunteers. There was a clear-cut increase in energy consumed by every individual from a free-choice buffet (mean increase 28 +/- 3.9%, p<0.001) during ghrelin compared with saline infusion. Visual analogue scores for appetite were greater during ghrelin compared to saline infusion. Ghrelin had no effect on gastric emptying as assessed by the paracetamol absorption test. Ghrelin is the first circulating hormone demonstrated to stimulate food intake in man. Endogenous ghrelin is a potentially important new regulator of the complex systems controlling food intake and body weight.

Glucagon-like peptide-1 7-36: a physiological incretin in man

The physiological role of glucagon-like peptide-1 7-36 amide (GLP-1 7-36) in man was investigated. GLP-1 7-36-like immunoreactivity was found in the human bowel; its circulating level rose after oral glucose and after a test breakfast. When it was infused into seven volunteers at a rate to mimic its postprandial plasma concentration in the fasting state, plasma insulin levels rose significantly and glucose and glucagon concentrations fell. During an intravenous glucose load, it greatly enhanced insulin release and significantly reduced peak plasma glucose concentrations, compared with a control saline infusion, even inducing postinfusion reactive hypoglycaemia. By comparison, infusion of glucose-dependent insulinotropic peptide (GIP) to physiological levels was less effective in stimulating insulin release. These observations suggest that GLP-1 7-36 is a physiological incretin and that it is more powerful than GIP. The observation of greatly increased postprandial plasma GLP-1 7-36 levels in patients with postgastrectomy dumping syndrome suggests that it may mediate the hyperinsulinaemia and reactive hypoglycaemia of this disorder.

Long-term persistence of hormonal adaptations to weight loss

BACKGROUND

After weight loss, changes in the circulating levels of several peripheral hormones involved in the homeostatic regulation of body weight occur. Whether these changes are transient or persist over time may be important for an understanding of the reasons behind the high rate of weight regain after diet-induced weight loss.

METHODS

We enrolled 50 overweight or obese patients without diabetes in a 10-week weight-loss program for which a very-low-energy diet was prescribed. At baseline (before weight loss), at 10 weeks (after program completion), and at 62 weeks, we examined circulating levels of leptin, ghrelin, peptide YY, gastric inhibitory polypeptide, glucagon-like peptide 1, amylin, pancreatic polypeptide, cholecystokinin, and insulin and subjective ratings of appetite.

RESULTS

Weight loss (mean [±SE], 13.5±0.5 kg) led to significant reductions in levels of leptin, peptide YY, cholecystokinin, insulin (P<0.001 for all comparisons), and amylin (P=0.002) and to increases in levels of ghrelin (P<0.001), gastric inhibitory polypeptide (P=0.004), and pancreatic polypeptide (P=0.008). There was also a significant increase in subjective appetite (P<0.001). One year after the initial weight loss, there were still significant differences from baseline in the mean levels of leptin (P<0.001), peptide YY (P<0.001), cholecystokinin (P=0.04), insulin (P=0.01), ghrelin (P<0.001), gastric inhibitory polypeptide (P<0.001), and pancreatic polypeptide (P=0.002), as well as hunger (P<0.001).

CONCLUSIONS

One year after initial weight reduction, levels of the circulating mediators of appetite that encourage weight regain after diet-induced weight loss do not revert to the levels recorded before weight loss. Long-term strategies to counteract this change may be needed to prevent obesity relapse. (Funded by the National Health and Medical Research Council and others; ClinicalTrials.gov number, NCT00870259.).

The effects of parathyroid hormone and alendronate alone or in combination in postmenopausal osteoporosis

BACKGROUND

Parathyroid hormone increases bone strength primarily by stimulating bone formation, whereas antiresorptive drugs reduce bone resorption. We conducted a randomized, double-blind clinical study of parathyroid hormone and alendronate to test the hypothesis that the concurrent administration of the two agents would increase bone density more than the use of either one alone.

METHODS

A total of 238 postmenopausal women (who were not using bisphosphonates) with low bone mineral density at the hip or spine (a T score of less than -2.5, or a T score of less than -2.0 with an additional risk factor for osteoporosis) were randomly assigned to daily treatment with parathyroid hormone (1-84) (100 microg; 119 women), alendronate (10 mg; 60 women), or both (59 women) and were followed for 12 months. Bone mineral density at the spine and hip was assessed by dual-energy x-ray absorptiometry and quantitative computed tomography. Markers of bone turnover were measured in fasting blood samples.

RESULTS

The bone mineral density at the spine increased in all the treatment groups, and there was no significant difference in the increase between the parathyroid hormone group and the combination-therapy group. The volumetric density of the trabecular bone at the spine increased substantially in all groups, but the increase in the parathyroid hormone group was about twice that found in either of the other groups. Bone formation increased markedly in the parathyroid hormone group but not in the combination-therapy group. Bone resorption decreased in the combination-therapy group and the alendronate group.

CONCLUSIONS

There was no evidence of synergy between parathyroid hormone and alendronate. Changes in the volumetric density of trabecular bone, the cortical volume at the hip, and levels of markers of bone turnover suggest that the concurrent use of alendronate may reduce the anabolic effects of parathyroid hormone. Longer-term studies of fractures are needed to determine whether and how antiresorptive drugs can be optimally used in conjunction with parathyroid hormone therapy.

Ghrelin causes hyperphagia and obesity in rats

Ghrelin, a circulating growth hormone-releasing peptide derived from the stomach, stimulates food intake. The lowest systemically effective orexigenic dose of ghrelin was investigated and the resulting plasma ghrelin concentration was compared with that during fasting. The lowest dose of ghrelin that produced a significant stimulation of feeding after intraperitoneal injection was 1 nmol. The plasma ghrelin concentration after intraperitoneal injection of 1 nmol of ghrelin (2.83 +/- 0.13 pmol/ml at 60 min postinjection) was not significantly different from that occurring after a 24-h fast (2.79 +/- 0.32 pmol/ml). After microinjection into defined hypothalamic sites, ghrelin (30 pmol) stimulated food intake most markedly in the arcuate nucleus (Arc) (0-1 h food intake, 427 +/- 43% of control; P < 0.001 vs. control, P < 0.01 vs. all other nuclei), which is potentially accessible to the circulation. After chronic systemic or intracerebroventricular (ICV) administration of ghrelin for 7 days, cumulative food intake was increased (intraperitoneal ghrelin 13.6 +/- 3.4 g greater than saline-treated, P < 0.01; ICV ghrelin 19.6 +/- 5.5 g greater than saline-treated, P < 0.05). This was associated with excess weight gain (intraperitoneal ghrelin 21.7 +/- 1.4 g vs. saline 10.6 +/- 1.9 g, P < 0.001; ICV ghrelin 15.3 +/- 4.3 g vs. saline 2.2 +/- 3.8 g, P < 0.05) and adiposity. These data provide evidence that ghrelin is important in long-term control of food intake and body weight and that circulating ghrelin at fasting concentrations may stimulate food intake.

Radioimmunological determination of human C-peptide in serum

A routing radioimmunoassay for human C-peptide in serum is described. Antibodies against human C-peptide were raised by immunizing guinea pigs with human b-component. Nine out of 12 animals produced useful antibodies within 6 months. Insulin antibodies coupled to Sepharose were used to bind human proinsulin and insulin in the serum and after centrifugation C-peptide was determined in the supernatant. The detection limit of the assay (calculated as 2 SD from zero) was about 0.003 pmole of C-peptide (in 100 mul). The main sources of error were: (1) Normal and diabetic sera devoid of C-peptide gave a displacement of 125I-Tyr-C-peptide varying from 0 to 0.16 nM (6 different antisera). Only one antiserum (M 1181) showed no displacement, and the values of C-peptide determined with this antiserum in normal and diabetic sera were lower than the values determined with another antiserum, which gave a value of 0.07 nM in the sera free of C-peptide. It is suggested that displacement found with most antisera is due to substances in serum that are not related to C-peptide or proinsulin. (2) Serial dilutions of pancreatic extracts and sera may yield dilution curves slightly different to those of the synthetic standard. Possible explanations are discussed. These sources of error can be eliminated or reduced by the proper selection of antisera. Fasting sera from 15 normals, 8 maturity-onset diabetics and 10 insulin-requiring diabetics showed the following concentrations of C-peptide: (M 1181) 0.35 +/- 0.09, 0.74 +/- 0.51 and 0.21 +/- 0.14 (nM, mean +/- SD). One hour after 1.75 g/kg oral glucose the values increased to 2.24 +/- 0.71, 2.34 +/- 0.24 nM.

Plasma ghrelin levels in lean and obese humans and the effect of glucose on ghrelin secretion

Ghrelin, a novel GH-releasing peptide isolated from human and rat stomach, stimulates food intake and GH secretion. We determined plasma ghrelin concentrations in patients with simple obesity, anorexia nervosa, and type 2 diabetes mellitus by RIA. We also studied plasma ghrelin responses to glucose load and meal intake and obtained a 24-h profile of circulating ghrelin in humans. Plasma ghrelin concentrations in patients with simple obesity and anorexia nervosa were lower and higher, respectively, than those of healthy subjects with normal body weight. Among those with type 2 diabetes mellitus, obese patients had lower and lean patients higher fasting plasma ghrelin concentrations than normal-weight patients. Fasting plasma ghrelin concentration was negatively correlated with body mass index in both nondiabetic and diabetic patients. Plasma ghrelin concentrations of normal subjects decreased significantly after oral and iv glucose administration; a similar response was also observed in diabetic patients after a meal tolerance test, reaching a nadir of 69% of the basal level after the meal. Circulating plasma ghrelin showed a diurnal pattern with preprandial increases, postprandial decreases, and a maximum peak at 0200 h. This study demonstrates that nutritional state is a determinant of plasma ghrelin in humans. Ghrelin secretion is up-regulated under conditions of negative energy balance and down-regulated in the setting of positive energy balance. These findings suggest the involvement of ghrelin in the regulation of feeding behavior and energy homeostasis.

Antidiabetogenic effect of glucagon-like peptide-1 (7-36)amide in normal subjects and patients with diabetes mellitus

BACKGROUND

Glucagon-like peptide-1 (7-36) amide (glucagon-like insulinotropic peptide, or GLIP) is a gastrointestinal peptide that potentiates the release of insulin in physiologic concentrations. Its effects in patients with diabetes mellitus are not known.

METHODS

We compared the effect of an infusion of GLIP that raised plasma concentrations of GLIP twofold with the effect of an infusion of saline, on the meal-related release of insulin, glucagon, and somatostatin in eight normal subjects, nine obese patients with non-insulin-dependent diabetes mellitus (NIDDM), and eight patients with insulin-dependent diabetes mellitus (IDDM). The blood glucose concentrations in the patients with diabetes were controlled by a closed-loop insulin-infusion system (artificial pancreas) during the infusion of each agent, allowing measurement of the meal-related requirement for exogenous insulin. In the patients with IDDM, normoglycemic-clamp studies were performed during the infusions of GLIP and saline to determine the effect of GLIP on insulin sensitivity.

RESULTS

In the normal subjects, the infusion of GLIP significantly lowered the meal-related increases in the blood glucose concentration (P less than 0.01) and the plasma concentrations of insulin and glucagon (P less than 0.05 for both comparisons). The insulinogenic index (the ratio of insulin to glucose) increased almost 10-fold, indicating that GLIP had an insulinotropic effect. In the patients with NIDDM, the infusion of GLIP reduced the mean (+/- SE) calculated isoglycemic meal-related requirement for insulin from 17.4 +/- 2.8 to 2.0 +/- 0.5 U (P less than 0.001), so that the integrated area under the curve for plasma free insulin was decreased (P less than 0.05) in spite of the stimulation of insulin release. In the patients with IDDM, the GLIP infusion decreased the calculated isoglycemic meal-related insulin requirement from 9.4 +/- 1.5 to 4.7 +/- 1.4 U. The peptide decreased glucagon and somatostatin release in both groups of patients. In the normoglycemic-clamp studies in the patients with IDDM, the GLIP infusion significantly increased glucose utilization (saline vs. GLIP, 7.2 +/- 0.5 vs. 8.6 +/- 0.4 mg per kilogram of body weight per minute; P less than 0.01).

CONCLUSIONS

GLIP has an antidiabetogenic effect, and it may therefore be useful in the treatment of patients with NIDDM:

Stomach is a major source of circulating ghrelin, and feeding state determines plasma ghrelin-like immunoreactivity levels in humans

Ghrelin, an endogenous ligand for the GH secretagogue receptor, was isolated from rat stomach and is involved in a novel system for regulating GH release. Although previous studies in rodents suggest that ghrelin is also involved in energy homeostasis and that ghrelin secretion is influenced by feeding, little is known about plasma ghrelin in humans. To address this issue, we studied plasma ghrelin-like immunoreactivity levels and elucidated the source of circulating ghrelin and the effects of feeding state on plasma ghrelin-like immunoreactivity levels in humans. The plasma ghrelin-like immunoreactivity concentration in normal humans measured by a specific RIA was 166.0 +/- 10.1 fmol/ml. Northern blot analysis of various human tissues identified ghrelin mRNA found most abundantly in the stomach and plasma ghrelin-like immunoreactivity levels in totally gastrectomized patients were reduced to 35% of those in normal controls. Plasma ghrelin-like immunoreactivity levels were increased by 31% after 12-h fasting and reduced by 22% immediately after habitual feeding. In patients with anorexia nervosa, plasma ghrelin-like immunoreactivity levels were markedly elevated compared with those in normal controls (401.2 +/- 58.4 vs. 192.8 +/- 19.4 fmol/ml) and were negatively correlated with body mass indexes. We conclude that the stomach is a major source of circulating ghrelin and that plasma ghrelin-like immunoreactivity levels reflect acute and chronic feeding states in humans.

Intravenous zoledronic acid in postmenopausal women with low bone mineral density

BACKGROUND

Bisphosphonates are effective agents for the management of osteoporosis. Their low bioavailability and low potency necessitate frequent administration on an empty stomach, which may reduce compliance. Gastrointestinal intolerance limits maximal dosing. Although intermittent intravenous treatments have been used, the optimal doses and dosing interval have not been systematically explored.

METHODS

We studied the effects of five regimens of zoledronic acid, the most potent bisphosphonate, on bone turnover and density in 351 postmenopausal women with low bone mineral density in a one-year, randomized, double-blind, placebo-controlled trial. Women received placebo or intravenous zoledronic acid in doses of 0.25 mg, 0.5 mg, or 1 mg at three-month intervals. In addition, one group received a total annual dose of 4 mg as a single dose, and another received two doses of 2 mg each, six months apart. Lumbar-spine bone mineral density was the primary end point.

RESULTS

There were similar increases in bone mineral density in all the zoledronic acid groups to values for the spine that were 4.3 to 5.1 percent higher than those in the placebo group (P<0.001) and values for the femoral neck that were 3.1 to 3.5 percent higher than those in the placebo group (P<0.001). Biochemical markers of bone resorption were significantly suppressed throughout the study in all zoledronic acid groups. Myalgia and pyrexia occurred more commonly in the zoledronic acid groups, but treatment-related dropout rates were similar to that in the placebo group.

CONCLUSIONS

Zoledronic acid infusions given at intervals of up to one year produce effects on bone turnover and bone density as great as those achieved with daily oral dosing with bisphosphonates with proven efficacy against fractures, suggesting that an annual infusion of zoledronic acid might be an effective treatment for postmenopausal osteoporosis.

Determinants of the impaired secretion of glucagon-like peptide-1 in type 2 diabetic patients

To elucidate the causes of the diminished incretin effect in type 2 diabetes mellitus we investigated the secretion of the incretin hormones, glucagon-like peptide-1 and glucose- dependent insulinotropic polypeptide and measured nonesterified fatty acids, and plasma concentrations of insulin, C peptide, pancreatic polypeptide, and glucose during a 4-h mixed meal test in 54 heterogeneous type 2 diabetic patients, 33 matched control subjects with normal glucose tolerance, and 15 unmatched subjects with impaired glucose tolerance. The glucagon-like peptide-1 response in terms of area under the curve from 0-240 min after the start of the meal was significantly decreased in the patients (2482 +/- 145 compared with 3101 +/- 198 pmol/liter.240 min; P = 0.024). In addition, the area under the curve for glucose-dependent insulinotropic polypeptide was slightly decreased. In a multiple regression analysis, a model with diabetes, body mass index, male sex, insulin area under the curve (negative influence), glucose-dependent insulinotropic polypeptide area under the curve (negative influence), and glucagon area under the curve (positive influence) explained 42% of the variability of the glucagon-like peptide-1 response. The impaired glucose tolerance subjects were hyperinsulinemic and generally showed the same abnormalities as the diabetic patients, but to a lesser degree. We conclude that the meal-related glucagon-like peptide-1 response in type 2 diabetes is decreased, which may contribute to the decreased incretin effect in type 2 diabetes.

Autoantibodies to a 140-kd polypeptide, CADM-140, in Japanese patients with clinically amyopathic dermatomyositis

OBJECTIVE

To identify novel autoantibodies specific for dermatomyositis (DM), especially those specific for clinically amyopathic DM (C-ADM).

METHODS

Autoantibodies were analyzed by immunoprecipitation in 298 serum samples from patients with various connective tissue diseases (CTDs) or idiopathic pulmonary fibrosis (IPF). Antigen specificity of the sera was further examined by immunoblotting and indirect immunofluorescence (IF). The disease specificity and clinical features associated with the antibody of interest were determined.

RESULTS

Eight sera recognized a polypeptide of approximately 140 kd (CADM-140 autoantigen) by immunoprecipitation and immunoblotting. Immunoreactivity was detected in the cytoplasm, and indirect IF revealed a granular or reticular pattern. Anti-CADM-140 antibodies were detected in 8 of 42 patients with DM, but not in patients with other CTDs or IPF. Interestingly, all 8 patients with anti-CADM-140 antibodies had C-ADM. Among 42 patients with DM, those with anti-CADM-140 autoantibodies had significantly more rapidly progressive interstitial lung disease (ILD) when compared with patients without anti-CADM-140 autoantibodies (50% versus 6%; P = 0.008).

CONCLUSION

These results indicate that the presence of anti-CADM-140 autoantibodies may be a novel marker for C-ADM. Further attention should be directed to the detection of rapidly progressive ILD in those patients with anti-CADM-140 autoantibodies.

Strategies to improve plasma half life time of peptide and protein drugs

Due to the obvious advantages of long-acting peptide and protein drugs, strategies to prolong plasma half life time of such compounds are highly on demand. Short plasma half life times are commonly due to fast renal clearance as well as to enzymatic degradation occurring during systemic circulation. Modifications of the peptide/protein can lead to prolonged plasma half life times. By shortening the overall amino acid amount of somatostatin and replacing L: -analogue amino acids with D: -amino acids, plasma half life time of the derivate octreotide was 1.5 hours in comparison to only few minutes of somatostatin. A PEG(2,40 K) conjugate of INF-alpha-2b exhibited a 330-fold prolonged plasma half life time compared to the native protein. It was the aim of this review to provide an overview of possible strategies to prolong plasma half life time such as modification of N- and C-terminus or PEGylation as well as methods to evaluate the effectiveness of drug modifications. Furthermore, fundamental data about most important proteolytic enzymes of human blood, liver and kidney as well as their cleavage specificity and inhibitors for them are provided in order to predict enzymatic cleavage of peptide and protein drugs during systemic circulation.

Biochemical markers of bone turnover, endogenous hormones and the risk of fractures in postmenopausal women: the OFELY study

The mechanisms leading to increased bone loss and skeletal fragility in women with postmenopausal osteoporosis are still poorly understood. Increased bone resorption, low serum estradiol and high serum sex-hormone-binding globulin (SHBG) recently have been reported as predictors of vertebral and hip fractures in elderly women. In a cohort of healthy untreated younger postmenopausal women aged 50-89 years (mean, 64 years), we compared baseline levels of bone markers and endogenous hormones in 55 women who subsequently had a fracture (20 vertebral and 35 peripheral fractures) with levels in the 380 women who did not fracture during a mean 5 years of follow-up. Women with levels in the highest quartile of four bone resorption markers including urinary-free deoxypyridinoline (D-Pyr), urinary type I collagen N-telopeptides (NTX), and urinary and serum type I collagen C-telopeptides (CTX) had about a 2-fold increased risk of fractures compared with women with levels in the three lowest quartiles with relative risk (RR) and 95% CI of 1.8 (1.0-3.4) for free D-Pyr, 1.7 (0.9-3.2) for urinary NTX, 2.3 (1.3-4.1) for urinary CTX, and 2.1 (1.2-3.8) for serum CTX. Serum levels of bone alkaline phosphatase (BAP) in the highest quartile were associated with an RR of fracture of 2.4 (1.3-4.2). Women with serum levels of estradiol and dehydroepiandrosterone (DHEA) sulfate in the lowest quartile had an RR of fracture of 2.2 (1.2-4.0) and 2.1 (1.2-3.8), respectively. Increased levels of SHBG and intact parathyroid hormone (PTH) were moderately associated with an increased risk of fracture. Similar results were obtained when the analysis was restricted to symptomatic vertebral and nonvertebral fractures. Adjustment of biochemical markers by hormone levels did not significantly alter the results. Women with both high bone resorption markers and low estradiol (or low DHEA sulfate) had a higher risk of fracture with RRs of 3.0-3.3 (p < 0.001). After adjustment for bone mineral density (BMD) of the hip, spine, radius, or total body, bone markers and hormones were still predictive of fracture risk with similar RRs. We conclude that high levels of some biochemical markers of bone turnover, low serum estradiol, low DHEA sulfate, high SHBG, and high PTH are associated with increased risk of osteoporotic fracture in postmenopausal women, independently of each other and of BMD. The mechanism by which some postmenopausal women have an increased rate of bone turnover leading to an increased risk of fracture remains to be elucidated.

Post-prandial decrease of circulating human ghrelin levels

Ghrelin, an endogenous ligand of the GH secretagogue-receptor, has recently been shown to stimulate GH secretion and to have orexigenic and adipogenic effects in rodents, but little is known about its regulation and biological function in humans. Gastric motor function is under control of the central nervous system; however, the afferent and efferent loops of this feedback control mechanism remain to be elucidated. In the study presented here we investigated the effect of nutrient intake on circulating human ghrelin levels, and a possible association between ghrelin levels and gastric emptying. Ten healthy volunteers received a standard meal after an overnight fast. Food intake significantly decreased plasma ghrelin levels from 248.5 +/- 15.0 to 179.5 +/- 17.9 fmol/ml (120 min after meal, p=0.047). Gastric emptying half-time (non-invasive 13C-octanoic acid breath test) was correlated with fasting plasma ghrelin levels (r=0.74, p=0.0013). Ghrelin appears to be one possible candidate to provide feedback signaling between nutrient intake, gastric motor function and the central nervous system.

Plasma N-terminal pro-brain natriuretic peptide and adrenomedullin: new neurohormonal predictors of left ventricular function and prognosis after myocardial infarction

BACKGROUND

Newly discovered circulating peptides, N-terminal pro-brain natriuretic peptide (N-BNP) and adrenomedullin (ADM), were examined for prediction of cardiac function and prognosis and compared with previously reported markers in 121 patients with myocardial infarction.

METHODS AND RESULTS

The association between radionuclide left ventricular ejection fraction (LVEF) and N-BNP at 2 to 4 days (r=-.63, P<.0001) and 3 to 5 months (r=-.58, P<.0001) after infarction was comparable to that for C-terminal BNP and far stronger than for ADM (r=-.26, P<.01), N-terminal atrial natriuretic peptide (N-ANP), C-terminal ANP, cGMP, or plasma catecholamine concentrations. For prediction of death over 24 months of follow-up, an early postinfarction N-BNP level > or = 160 pmol/L had sensitivity, specificity, positive predictive value, and negative predictive values of 91%, 72%, 39%, and 97%, respectively, and was superior to any other neurohormone measured and to LVEF. Only 1 of 21 deaths occurred in a patient with an N-BNP level below the group median (Kaplan-Meier survival analysis, P<.00001). For prediction of heart failure (left ventricular failure), plasma N-BNP > or = 145 pmol/L had sensitivity (85%) and negative predictive value (91%) comparable to the other cardiac peptides and was superior to ADM, plasma catecholamines, and LVEF. By multivariate analysis, N-BNP but not ADM provided predictive information for death and left ventricular failure independent of patient age, sex, LVEF, levels of other hormones, and previous history of heart failure, myocardial infarction, hypertension, or diabetes.

CONCLUSIONS

Plasma N-BNP measured 2 to 4 days after myocardial infarction independently predicted left ventricular function and 2-year survival. Stratification of patients into low- and high-risk groups can be facilitated by plasma N-BNP or BNP measurements, and one of these could reasonably be included in the routine clinical workup of patients after myocardial infarction.

Type beta transforming growth factor in human platelets: release during platelet degranulation and action on vascular smooth muscle cells

A specific radioimmunoassay for type beta transforming growth factor (TGF-beta) was developed and used to show that human platelets treated with thrombin release TGF-beta as a consequence of degranulation. The thrombin concentrations required to induce release of TGF-beta parallel those concentrations that release the alpha-granule marker, beta-thromboglobulin. Related studies showed that TGF-beta acts on early passage, explant cultures of bovine aortic smooth muscle cells by inhibiting the effect of mitogens on proliferation of subconfluent cell monolayers yet synergizing with mitogens to stimulate growth of the same cells when cultured in soft agar. The results show that primary cultures of bovine aortic smooth muscle cells and established normal rat kidney cells behave similarly with regard to TGF-beta action. Moreover, the data suggest that platelet-mediated proliferation of aortic smooth muscle cells in vivo may not result solely from the stimulatory effect of platelet-derived growth factor (PDGF), but rather from an interaction of platelet factors which has the intrinsic ability to limit as well as stimulate mitosis.