Therapeutic efficacy of a soluble receptor activator of nuclear factor kappaB-IgG Fc fusion protein in suppressing bone resorption and hypercalcemia in a model of humoral hypercalcemia of malignancy

Receptor activator of nuclear factor kappaB (RANK) is a membrane-bound tumor necrosis factor receptor homologue that mediates signals obligatory for osteoclastogenesis as well as osteoclast activation and survival in vivo. The present study was undertaken to evaluate the efficacy of a soluble murine RANK-human immunoglobulin fusion protein (muRANK.Fc) as a bone resorption inhibitor in vitro and in vivo. The in vitro studies demonstrated the ability of muRANK.Fc to inhibit human parathyroid hormone-related protein (PTHrP)-induced resorption in fetal rat long bone cultures. Short-term administration of muRANK.Fc to normal growing mice resulted in a complete disappearance of osteoclasts from metaphyses of long bones associated with a pronounced increase in calcified trabeculae and bone radiodensity. In a model of humoral hypercalcemia of malignancy in which PTHrP secreted by s.c. xenografts of human lung cancer in nude mice induces extensive osteolysis and severe hypercalcemia, daily administration of muRANK.Fc from time of tumor implantation profoundly inhibited osteoclastic bone resorption and prevented hypercalcemia. muRANK.Fc had no effect on tumor production of PTHrP, because there was no significant difference between circulating human PTHrP levels in muRANK.Fc-treated and vehicle-treated tumor-bearing mice. Moreover, even when treatment was initiated after hypercalcemia was established, muRANK.Fc significantly attenuated further increases in blood ionized calcium. These data demonstrate the potent antiresorptive effects of muRANK.Fc in vivo as well as highlight the potential utility of disrupting RANK signaling as a novel therapeutic approach in humoral hypercalcemia of malignancy and possibly multiple myeloma and skeletal metastases associated with osteolysis.

A role for N-cadherin in the development of the differentiated osteoblastic phenotype

Cadherins are a family of cell surface adhesion molecules that play an important role in tissue differentiation. A limited repertoire of cadherins has been identified in osteoblasts, and the role of these molecules in osteoblast function remains to be elucidated. We recently cloned an osteoblast-derived N-cadherin gene from a rat osteoblast complementary DNA library. After in situ hybridization of rat bone and immunohistochemistry of human osteophytes, N-cadherin expression was localized prominently in well-differentiated (lining) osteoblasts. Northern blot hybridization in primary cultures of fetal rat calvaria and in human SaOS-2 and rat ROS osteoblast-like cells showed a relationship between N-cadherin messenger RNA expression and cell-to-cell adhesion, morphological differentiation, and alkaline phosphatase and osteocalcin gene expression. Treatment with a synthetic peptide containing the His-Ala-Val (HAV) adhesion motif of N-cadherin significantly decreased bone nodule formation in primary cultures of fetal rat calvaria and inhibited cell-to-cell contact in rat osteoblastic TRAB-11 cells. HAV peptide also regulated the expression of specific genes such as alkaline phosphatase and the immediate early gene zif268 in SaOS-2 cells. Transient transfection of SaOS-2 cells with a dominant-negative N-cadherin mutant (NCADdeltaC) significantly inhibited their morphological differentiation. In addition, aggregation of NCTC cells derived from mouse connective tissue stably transfected with osteoblast-derived N-cadherin was inhibited by either treatment with HAV or transfection with NCADdeltaC. Together, these results strongly support a role for N-cadherin, in concert with other previously identified osteoblast cadherins, in the late stages of osteoblast differentiation.

Covalent immobilization of recombinant human alphavbeta3 integrin on a solid support with retention of functionality

Alphavbeta3 is the major receptor mediating the attachment of osteoclasts to bone surface and plays a critical role in bone resorption and remodeling. Interfering with alphavbeta3 binding inhibits osteoclast-mediated bone resorption, and thus demonstrates the potential utility of alphavbeta3 antagonists for therapy of osteoporosis. This report describes the generation of an alphavbeta3 affinity column which was created to enable screening of collections of large numbers of ligands, e.g., combinatorial libraries (previously prepared by us), to sort and identify ligands with the highest affinity for alphavbeta3. We demonstrate that covalent immobilization of the heterodimeric alphavbeta3 receptor can be achieved with retention of characteristic ligand binding properties. Human alphavbeta3 was isolated from human embryonic kidney cells (HEK 293) that stably express high levels of the recombinant receptor and then affinity purified to homogeneity. Purified alphavbeta3 receptor was linked covalently to activated CH-Sepharose 4B beads. Quantification of immobilized functional receptor was determined by Scatchard analysis. The immobilized functional receptor maintains binding properties similar to the membrane-embedded and soluble receptor. The immobilized receptor also can be used to select the highest affinity ligand from among a mixture of peptides which differ in their binding affinity, structure, and hydrophobicity, both when the peptides are loaded in equimolar concentrations in a mixture and when the concentration of the highest affinity ligand is reduced 10-fold. Liquid chromatography-mass spectrometry was utilized to confirm selective ligand binding and to demonstrate that preferential binding was not due to nonspecific hydrophobic interactions with immobilized alphavbeta3 receptor or the affinity column. This approach may be of general use for affinity-based screening of ligands for other integrins and should enable practical screening of combinatorial libraries containing large numbers of potential ligands for the human alphavbeta3 integrin receptor, including linear peptides, cyclic peptides, and peptidomimetics.

5-Lipoxygenase metabolites inhibit bone formation in vitro

The leukotrienes and peptido-leukotrienes are 5-lipoxygenase (5-LO) metabolites of arachidonic acid that appear to have unique effects on bone, distinct from those of the prostaglandins. Application of exogenous leukotrienes in vitro and in vivo results in increased osteoclast formation and bone resorption. While 5-LO metabolites of arachidonic acid clearly stimulate osteoclastic bone resorption, little is known concerning their effects on osteoblastic bone formation. We examined the effects of the 5-LO metabolites 5-HETE, the leukotriene LTB4 and, as representative of the peptido-leukotrienes, LTD4 on the formation of mineralized nodules of fetal rat calvarial cells in the presence of dexamethasone and recombinant human bone morphogenetic protein-2 (rhBMP-2). We also examined the effects of these 5-LO metabolites on alkaline phosphatase activity and cell proliferation in these cultures and the effects of 5-HETE and LTB4 on cultured explants of neonatal murine calvariae. We found that the bone-forming capacity of osteoblasts was impaired when cells were cultured in the presence of 5-LO metabolites. These data indicate that metabolites of the 5-LO pathway are negative regulators of bone formation. The continued presence of these metabolites in the bone environment might account, in part, for the bone loss associated with chronic inflammatory conditions.

Abnormal glucose tolerance and other coronary heart disease risk factors in an isolated aboriginal community in central Australia

OBJECTIVE

To determine the age- and sex-specific prevalence of diabetes, impaired glucose tolerance (IGT), and coronary heart disease risk factors in a remote central Australian Aboriginal community maintaining some degree of traditional lifestyle, living in homeland communities on their ancestral land.

RESEARCH DESIGN AND METHODS

A cross-sectional survey of 437 subjects > or = 15 years of age (189 men, 248 women), representing 80% of the adult population residing in the community at the time of the survey, was performed and the following parameters measured: BMI, glucose tolerance, circulating insulin and lipids, and blood pressure.

RESULTS

The mean BMI for this population was 22.9 +/- 4.8 kg/m2. The prevalence of diabetes in the age group of 15-34 years (103 men and 140 women) was 2 and 6% for men and women, respectively. In the 35-years-and-older age group (86 men and 108 women), diabetes prevalence was 19 and 13% for men and women, respectively. Over half the diabetic subjects did not exhibit fasting hyperglycemia. IGT occurred in 8 and 15% of younger men and women, respectively, and in 17 and 32% of older men and women, respectively. Smoking was common among men (53% current smokers) but rare among women (2% current smokers). The prevalence of hypercholesterolemia, hypertriglyceridemia, hypertension, and overweight rose with increasing degrees of glucose intolerance. The two communities adjacent to the only store in the area had a higher prevalence of abnormal glucose tolerance than did the more remote homeland communities (odds ratio for abnormal glucose tolerance: 2.92; 95% CI 1.51-5.63).

CONCLUSIONS

Despite their relative leanness, this Aboriginal population exhibited relatively high prevalences of IGT and diabetes without fasting hyperglycemia. The data suggest a protective effect of a decentralized mode of living, as opposed to a more urbanized lifestyle, on the occurrence of glucose intolerance. Abnormal lipid profiles (particularly high triglycerides and low HDL cholesterol) and the high prevalence of smoking in men indicated a high-risk profile for coronary heart disease in this population.

Regulation of osteopontin expression by type I collagen in preosteoblastic UMR201 cells

When UMR201 cells, phenotypically preosteoblastic, were placed onto a type I collagen gel, expression of osteopontin (OP) mRNA and protein were strongly upregulated, compared to cells plated onto plastic. This upregulation was dose-dependent, with respect to the concentration of collagen gel, and was observable within hours of cells having attached and spread on the substrate. Retinoic acid (RA) acted synergistically with type I collagen at each concentration to induce a much greater increase in OP mRNA than in cells on plastic. In addition, RA increased the phosphorylation of secreted OP. The exogenous collagen substrate inhibited the growth of UMR201 cells, with the extent and duration of inhibition dependent on the collagen concentration. The effect of type I collagen was specific; plating cells on fibronectin, laminin or vitronectin did not upregulate OP expression. In contrast to the effects on OP expression, the strong RA induction of alkaline phosphatase (ALP) mRNA in cells on plastic was attenuated in cells plated on type I collagen. Growth on type I collagen did not change OP mRNA stability or transcription rate, although there was decreased stability of the ALP mRNA in cells on collagen.

Expression of parathyroid hormone-related protein in cells of osteoblast lineage

The expression of parathyroid hormone-related protein (PTHrP) was studied in a range of cell cultures representative of the osteoblast lineage and in rat calvarial sections. Primary newborn rat calvarial cells, a rat preosteoblastic cell line (UMR 201), a mouse stromal cell line (ST 2), a mouse calvaria-derived osteoblastic cell line (KS 4), and rat osteosarcoma cell lines (UMR 106-01 and -06), all expressed PTHrP when examined by reverse transcription polymerase chain reaction (RT-PCR). Using a radioimmunoassay we also demonstrated PTHrP in the conditioned medium of the cultured cells, with the exception of UMR 106-01 and -06 cells. Treatment of UMR 201 cells with all-trans-retinoic acid which induces them to acquire a more differentiated phenotype, also led to a time-dependent decrease in PTHrP mRNA levels as determined by RT-PCR, Northern blot analysis, and in situ hybridization. Decreased PTHrP levels in the conditioned medium of the treated cells was also observed. These results suggested that PTHrP production might be greater in less mature osteoblasts. Examination of the populations obtained from newborn rat calvariae by sequential collagenase digestion revealed that the early digests exhibited low ALP activity, low expression of PTH/PTHrP receptor mRNA, and no adenylate cyclase response to PTHrP(1-34). These populations showed the highest level of mRNA and production of PTHrP. Cells from later digests, the "osteoblast-rich" populations, had reduced PTHrP expression. Immunohistochemistry and in situ hybridization in sections of newborn rat calvariae showed PTHrP expression in cuboidal osteoblasts located adjacent to bone and in spindle-shaped cells in the periosteal region. It is concluded that PTHrP is produced by cells of the osteoblast lineage, supporting the hypothesis that PTHrP may function physiologically as a paracrine factor in bone.

Modulation of the signal recognition particle 54-kDa subunit (SRP54) in rat preosteoblasts by the extracellular matrix

Rat preosteoblastic cells, UMR201, develop a more mature phenotype when subcultured onto a type I collagen gel when compared with their growth on plastic. Basal osteopontin mRNA expression is up-regulated, whereas retinoic acid-induced alkaline phosphatase expression is reduced in cells on collagen when compared with cells plated onto plastic. We have used differential display polymerase chain reaction (PCR) of mRNA to identify other mRNA species that are regulated by collagen and/or retinoic acid in UMR201 cells. A number of differentially expressed PCR products were isolated, whose sequences did not correspond to known sequences in the data bank. However, one species which was up-regulated by growth on collagen showed 95 and 94% homology to the murine and canine 54-kDa subunit of the signal recognition particle (SRP54), respectively. In time course experiments, using reverse transcription PCR, it was found that SRP54 mRNA was up-regulated in UMR201 cells as early as 1 h after subculture onto collagen, when compared with cells subcultured onto plastic, and levels remained elevated after 48 h. The increased expression of SRP54 paralleled the increased expression of a known secreted protein, osteopontin. SRP54 recognizes signal sequences of proteins destined for secretion and retards them for further elongation in the endoplasmic reticulum. The increased expression may correlate with the synthesis of specific extracellular matrix molecules in differentiating osteoblasts.

Cell substratum modulates responses of preosteoblasts to retinoic acid

The aim of this study was to determine the role of ECM components of bone in regulating the differentiation and function of cells of the osteoblast lineage. Rat UMR 201 cells, phenotypically preosteoblast, were plated onto plastic tissue culture dishes or dishes coated with gelled type I collagen or reconstituted basement membrane (matrigel). Acute cell attachment assays showed that cells adhered to substrates in the following order: collagen > matrigel >> plastic. Proliferation rate up to 96 hr were similar on each substrate. However, if cells were treated with 10(-6) M retinoic acid (RA), proliferation rates were reduced compared with control for cells grown on collagen and matrigel but not on plastic. Morphological changes were matrix-specific; in subconfluent cultures, long thin processes were seen with cells grown on collagen and a pattern of interconnecting cell processes formed when cells were plated on matrigel. Striking differences were observed in the constitutive or RA-induced gene expression of cells grown on the different substrates. When cells plated on collagen were treated with RA, induction of mRNA for alkaline phosphatase (ALP) as well as ALP enzyme activity were much less than with cells grown on plastic. In contrast, RA treatment induced osteopontin (OP) mRNA expression more strongly in cells plated on collagen compared with plastic within 24 hr and this was maintained for 72 hr. RA treatment produced a two fold increase of pro-alpha 1(I) collagen mRNA in cells grown on plastic and matrigel but not in cells grown on collagen. Growth on collagen produced changes in the way UMR 201 cells responded to RA from which they did not fully recover in subsequent 48-hr growth periods on plastic. These results indicate that ECM components regulate the function of and are capable of modulating RA-induced differentiation of preosteoblasts.

Obesity, diabetes, and hyperlipidemia in a central Australian aboriginal community with a long history of acculturation

OBJECTIVE

To determine the age- and sex-specific prevalence of diabetes and to examine associations between related anthropometric and metabolic abnormalities in an Aboriginal community in central Australia with a long history of acculturation.

RESEARCH DESIGN AND METHODS

We used a cross-sectional survey of 353 adults > 15 yr of age (87% response rate) and measured the following parameters: weight, height, circumferences of waist and hips; glucose, insulin, cholesterol, triglyceride, and high-density lipoprotein cholesterol in fasting plasma; and plasma glucose and insulin 2 h after 75 g oral glucose.

RESULTS

The prevalence of diabetes was 29.6% in survey participants > 35 yr of age and 5.3% in those < 35 yr of age. Impaired glucose tolerance also occurred with higher frequency in those > 35 yr of age (14.8 vs. 4.7%). Of those > 35 yr of age, 75% of the women and 51% of the men were overweight or obese, with a body mass index > or = 25 kg/m2. A large insulin response to oral glucose was evident, with the upper tertile of the 2-h insulin response six times higher than the lower tertile (113 +/- 43 vs. 19 +/- 8 mU/L). Hyperinsulinemia showed a strong, positive association with impaired glucose tolerance, body mass index, waist-to-hip ratio, cholesterol, and triglyceride levels and a negative association with high-density lipoprotein cholesterol levels. Cholesterol levels were on average 0.5 mM higher in men than in women. Deteriorations in carbohydrate and lipid metabolism occurred before 40 yr of age: diabetes, body mass index, waist-to-hip ratio, and fasting triglycerides and cholesterol concentrations peaked and high-density lipoprotein cholesterol concentrations reached their nadir at the end of the fourth decade.

CONCLUSIONS

These data suggest that any intervention programs developed to prevent or reduce diabetes prevalence in this population should be targeted at adolescents and young adults.

Low-dose acarbose improves glycemic control in NIDDM patients without changes in insulin sensitivity

OBJECTIVE

To examine the impact on metabolic control in NIDDM patients of the alpha-glucosidase inhibitor, acarbose, when administered at a low dose in powdered form.

RESEARCH DESIGN AND METHODS

Six subjects were recruited for a double-blind cross-over trial using 25 mg powdered acarbose and a placebo 3 times a day with meals for 3 mo. In addition to parameters of diabetes control and body weight, glucose turnover and insulin sensitivity were measured with the hyperinsulinemic/euglycemic clamp technique combined with tracer kinetics.

RESULTS

None of the subjects showed significant changes in FPG levels or body weight either on the 3-mo course of acarbose or placebo. HbA1c fell significantly from 10.6 +/- 1.0 to 9.4 +/- 1.3% (P = 0.05) during treatment with acarbose but failed to change on placebo (10.1 +/- 1.0 to 11.1 +/- 2.0%; P = 0.36). Basal HGP and glucose utilization were unchanged during either of the treatment periods, and hyperinsulinemia produced a similar degree of suppression of HGP before and after each treatment. At a physiological concentration, insulin failed to stimulate glucose clearance in these diabetic patients, and no improvement was seen with acarbose treatment. No changes in plasma lipids or lipoprotein profiles were demonstrated after 3 mo on acarbose. In acute studies, it was shown that administration of acarbose at a dose of 25 mg powder per meal significantly decreased the postprandial glycemic excursion.

CONCLUSIONS

When administered in the powdered form at the low dose of 25 mg 3 times/day with meals over 3 mo, acarbose was well tolerated by the NIDDM patients and was without side effects. It improved glycemic control by reducing postprandial hyperglycemia, but had no effect on glucose turnover, insulin sensitivity, or lipid profile.

Effect of fatty acid oxidation inhibition on glucose metabolism in diabetic rats

Inhibition of fatty acid (FA) oxidation has been shown previously to lower blood glucose levels acutely in diabetic rats. However, the longer term effects of FA oxidation inhibition have not been determined. This study examines the effect of inhibition of (FA) oxidation for 3 weeks on carbohydrate metabolism in rats rendered diabetic with streptozotocin (STZ). STZ treated rats (50 mg/kg) were randomized into 3 groups: a non-treated diabetic group and 2 groups treated with either 12.5 or 25 mg/kg/day Etomoxir (a specific carnitine palmitoyl transferase inhibitor) for 3 weeks. The 3 groups of rats had ad libitum access to a high fat diet (50% energy fat, 30% carbohydrate and 20% protein) throughout the study. After 3 weeks hepatic glucose production (HGP) was estimated using a constant infusion of (3H)-6-glucose in-vivo after an overnight fast. Inhibition of FA oxidation in diabetic rats resulted in a significant reduction in fasting glucose levels and hepatic glucose production. In addition, experiments with adipocytes isolated from diabetic rats treated with etomoxir demonstrated an increase in sensitivity and responsiveness to insulin of glucose utilization and pyruvate dehydrogenase (PDH) activity. It is important to note that these improvements in carbohydrate metabolism were not accompanied by increases in circulating FFA or triglyceride levels which were unchanged or lower after inhibition of FA oxidation.

Identification of early metabolic defects in diabetes-prone Australian aborigines

The aim of the present study was to identify in young, diabetes-prone subjects the early abnormalities which may predispose to the development of type 2 diabetes. We studied 10 full-blood Australian Aborigines all of whom had a family history of diabetes and who were from an urbanised community with a high prevalence of this disorder. They were compared to 10 age- and body-mass-index-matched Caucasian controls with no family history of diabetes. Glucose kinetics were measured basally and following an oral glucose load. Fasting plasma glucose was equal in the two groups, but 2 h following the 75 g glucose load, the Aboriginal subjects had higher glycaemia than the controls (P less than 0.01). Insulinaemia was higher in the Aborigines both basally and following the glucose drink (P less than 0.05). Despite the hyperinsulinaemia, hepatic glucose production was higher in the Aboriginal subjects (P less than 0.01), while metabolic clearance rate was lower. It is concluded that in young Australian Aborigines with a strong family history of type 2 diabetes, both hepatic and peripheral insulin resistance are early abnormalities.

A high-fat diet worsens metabolic control in streptozotocin-treated rats by increasing hepatic glucose production

The aim of this study was to determine the mechanism by which a high-fat diet exacerbates the diabetes produced by a low dose of streptozotocin (STZ). The glucose clamp technique was used to determine hepatic glucose production (HGP) and the disappearance rate (Rd) of glucose, basally and during insulin infusions of 1.0 and 3.0 mU/kg/min in control of STZ-treated rats fed either a low-fat or high-fat diet. Fasting plasma glucose in the high fat-STZ (HFS) group was significantly higher than in any of the other groups: low fat-STZ (LFS), high-fat controls (HFC), or low-fat controls (LFC) (18.1 +/- 1.6 v 8.1 +/- 0.8 mmol/L, P less than .001; 6.0 +/- 0.2 mmol/L, P less than .001; 5.4 +/- 0.1 mmol/L, P less than .001, respectively). Basal HGP was markedly higher in the HFS group compared with each of the other three groups (98.8 +/- 5.9 v 61.4 +/- 3.7, P less than .001; 42.9 +/- 1.6, P less than .001; 39.6 +/- 1.3 mumol/kg/min, P less than .001; HFS v LFS, HFC, and LFC, respectively). Following insulin infusion, no differences were observed in HGP between the LFC and LFS groups at either insulin dose. However, HGP was not suppressed to control levels in either of the high-fat diet groups, and this defect was more marked in the HFS group. It is concluded that a high-fat diet exacerbates mild STZ diabetes primarily by increasing HGP.

Cholesterol-lowering effect of a low-fat diet containing lean beef is reversed by the addition of beef fat

The aim of this study was to differentiate between lean beef and beef fat as risk factors for elevated plasma cholesterol concentrations. Ten healthy weight-stable subjects (five men, five women) participated. Energy intake was kept constant over the 5-wk study. Total cholesterol concentrations fell significantly within 1 wk of commencing the very-low fat (9%) energy from fat) lean-beef (500 g/d) diet (5.91 +/- 0.47 to 4.72 +/- 0.42 mmol/L, p less than 0.001) and rose as beef drippings were added in a stepwise manner in weeks 4 and 5 (5.45 +/- 0.56 mmol/L in week 5). The changes in total cholesterol concentrations were due almost entirely to changes in the concentration of low-density lipoprotein cholesterol levels. These results indicate that it is the beef fat, not lean beef itself, that is associated with elevations in cholesterol concentrations and that lean beef can be included in cholesterol-lowering diets provided it is free of all visible fat and the saturated fatty acid content of the diet is low.

Ingestion of different types of fat in the evening meal does not affect metabolic responses to a standard breakfast

High-fat diets produce insulin resistance, but it is not known how quickly changes become evident or whether different types of fat produce different responses. The aim of this study was to determine whether a high-fat evening meal affected glucose response to a standard breakfast 12 h later. On six occasions eight weight-stable subjects consumed a standard evening meal (109 g carbohydrate, 27 g protein, 6 g fat, and 10.6 g fiber) that was either unsupplemented or supplemented with 41 g fat (safflower oil, olive oil, butter, or medium-chain triglyceride) or 75 g carbohydrate followed by a standard breakfast. Glucose, insulin, and free fatty acid responses were measured over 3 h. There were no differences in metabolic responses to the standard breakfast after the different evening meals, indicating that a single high-fat meal has no deleterious effects on carbohydrate metabolism 12 h later, regardless of the type of fat ingested.

Diabetes, hyperinsulinemia, and hyperlipidemia in small aboriginal community in northern Australia

A small rural Aboriginal community in northern Australia was surveyed for diabetes, impaired glucose tolerance (IGT), hyperinsulinemia, and lipid levels. Of the 122 adults greater than 17 yr of age who participated (95% response rate), 11.5% had diabetes, 7.4% had IGT, and the remaining 81.1% had normal glucose tolerance. Both diabetes and IGT were strongly age related. This high frequency of diabetes occurred, despite the population being relatively lean. Although the body mass index (BMI) increased with age in both men and women, only 25% of the population overall had BMI greater than 25 kg/m2. There were wide ranges of insulin responses to glucose, with the upper tertile of 2-h insulin levels being more than seven times higher than the lower tertile (144 +/- 13 vs. 19 +/- 1 mU/L). Hyperinsulinemia was associated with IGT, elevated triglycerides, and lower high-density lipoprotein cholesterol levels. Lipid abnormalities were much more frequent among men than women. Cholesterol levels were an average of 0.55 mM higher and triglycerides an average of 1.05 mM higher in men than in women, and both increased with age. In conclusion, this small isolated Aboriginal population from northern Australia had an unexpectedly high frequency of diabetes (in view of their relative leanness) in association with a high frequency of metabolic abnormalities indicative of insulin resistance (hyperinsulinemia, IGT, hypertriglyceridemia).

The effects of diet differing in fat, carbohydrate, and fiber on carbohydrate and lipid metabolism in type II diabetes

This study was designed to determine the effects of varying the proportions of carbohydrate, fiber, and fat on metabolic control in Type II diabetes. Ten men, aged 50 to 69 years, with Type II diabetes participated. Four isocaloric diets were consumed for 2 weeks each, with a break of 6 to 14 weeks between diets to ensure no carryover effects. Two of the diets were high in carbohydrate (63% to 65% energy) and low in fat (10% to 12% energy) but differed in their fiber contents (20 vs. 45 gm/day). The other two diets were low in carbohydrate (23% to 27% energy) with either a low or a high fat content (15% vs. 55% energy) and a high or normal protein content (62% vs. 18% energy). The composition of the subjects' usual diets in the week before each of the experimental diets did not vary significantly: carbohydrate 47% to 50% energy, protein 22% to 25% energy, fat 27% to 31% energy, and fiber 24 to 25 gm/day. A 75-gm oral glucose tolerance test and a 12-hour metabolic profile in response to 3 meals typical of the particular diet were conducted before and at the conclusion of each 2-week dietary period. The most significant improvements in metabolic control (as assessed by the effects of the diets on fasting glucose and on lipids, and on the glucose and insulin responses to oral glucose and the mixed meals) were obtained with the high-fiber, high-carbohydrate, low-fat diet and with the low-carbohydrate, high-protein, low-fat diet. Metabolic control was not significantly affected by the low-fiber, high-carbohydrate, low-fat diet, but it deteriorated significantly on the low-carbohydrate, high-fat diet. The results of this study confirmed the importance of high fiber and low fat in improving metabolic control in Type II diabetes. In conclusion, if high-carbohydrate, low-fat diets are to be recommended to patients with diabetes, it is essential that the type of carbohydrate recommended be unrefined and high in fiber.

Impaired glucose tolerance, hyperinsulinemia, and hypertriglyceridemia in Australian aborigines from the desert

A cross section of adult full-blooded Aborigines from three small isolated communities in the desert region of northwest Australia was surveyed for diabetes, impaired glucose tolerance (IGT), insulin levels, and lipoprotein lipids. Sixty-three men and 86 women from a total adult population of 330 were tested. Of the people tested, 67.6% had normal glucose tolerance, 25% had IGT, and 7.4% had diabetes. Both diabetes and IGT were strongly age related. Fasting insulin levels and insulin responses to oral glucose (elevation above basal) were elevated. Although fasting insulin rose with age, insulin response did not rise after adjustment for body mass index (BMI). Plasma triglyceride levels were high, particularly in men greater than 35 yr old (3.13 +/- 0.32 mM), but cholesterol levels were not elevated. Multiple regression analysis of fasting glucose, 2-h glucose, plasma triglyceride, fasting insulin, and insulin response for the nondiabetic subjects revealed 1) BMI was an independent risk factor for elevated 2-h glucose levels in women but not in men and was strongly related to fasting insulin concentrations in both genders; 2) fasting insulin concentration was an independent risk factor for increases in fasting glucose, insulin response, and triglyceride levels; 3) insulin response was related to the 2-h glucose level; 4) fasting and 2-h glucose levels and fasting insulin and triglyceride concentrations all rose with age in both genders, with the rate of increase generally greater in men. The most striking difference between these desert Aborigines and previously studied coastal Aborigines from the same geographical region was the significantly higher insulin response.(ABSTRACT TRUNCATED AT 250 WORDS)

Commercial canning increases the digestibility of beans in vitro and postprandial metabolic responses to them in vivo

Six weight-stable subjects consumed three test meals containing 50 g carbohydrate in random order after a 12-h fast: D-glucose, canned baked beans, or home-cooked (boiled) baked beans. Postprandial glucose and insulin responses were greatest to glucose, lowest to home-cooked baked beans, and intermediate to canned baked beans. Profiles of glucose and insulin responses to home-cooked beans were flatter and more attenuated than responses to canned beans or glucose, which correlates with the in vitro data showing a six-to-eight times higher rate of starch hydrolysis in canned beans relative to boiled beans. Increases in temperature (pressure) and duration of pressure-cooking resulted in increased starch digestibility, whereas even mildly acidic conditions (pH 5.0) markedly reduced it. None of the processes studied affected the total amount of available carbohydrate.

Factors affecting the rate of hydrolysis of starch in legumes

In an attempt to understand the mechanism for the extremely slow rate of digestion and absorption of carbohydrate from legumes, we have examined a number of factors which could potentially affect the process in vitro. The rate of hydrolysis of legume starch in vitro was not affected by the presence of fat (as either butter or an emulsion). However, it was significantly increased in commercially available canned bean preparations, suggesting that the high temperatures used in the canning process may alter the availability of starch in legumes. In vitro starch hydrolysis rate was also significantly increased by grinding legumes finely prior to cooking. Finally, the slow rate of digestion and absorption of legume carbohydrate does not appear to be due to viscosity since a) increasing the shaking rate of viscous mixture of either red kidney beans or lentils from 0 to 120 oscillations per minute did not affect the hydrolysis rate, and b) a thick viscous mixture of either of these legumes did not retard the diffusion of free glucose from a dialysis sac into the dialysate.