Enantioselective carbenoid insertion into C(sp(3))-H bonds.

The enantioselective carbenoid insertion into C(sp(3))-H bonds is an important tool for the synthesis of complex molecules due to the high control of enantioselectivity in the formation of stereogenic centers. This paper presents a brief review of the early issues, related mechanistic studies and recent applications on this chemistry area.

Leptin concentrations in Prader-Willi syndrome before and after growth hormone replacement.

OBJECTIVE: This study explored leptin concentrations in Prader-Willi syndrome (PWS), a genetic disorder characterized by significant obesity and presumed hypothalamic dysfunction. The potential interaction of leptin metabolism with the growth hormone (GH) axis was also studied. STUDY DESIGN: Plasma leptin concentrations and percent body fat were determined by radioimmunoassay and dual energy x-ray absorptionmetry, respectively, in 23 children with Prader-Willi syndrome and 23 children with exogenous obesity. RESULTS: Log plasma leptin concentrations were positively correlated with percentage body fat in PWS (r = 0.844) and exogenous obesity (r = 0.869). When the regression lines for the two groups were compared, there were no differences in their slopes (P = 0.737) or intercepts (P = 0.701). Administration of recombinant human growth hormone to PWS children for 12 months significantly reduced both percentage body fat and plasma leptin concentrations, but the relationship of log plasma leptin to percentage body fat was unchanged. CONCLUSION: Prader-Willi syndrome is not accompanied by deranged leptin concentrations and there was no evidence of an interaction of the GH axis with leptin metabolism in these GH-deficient children.

Experiment and theory highlight role of native state topology in SH3 folding.

We use a combination of experiments, computer simulations and simple model calculations to characterize, first, the folding transition state ensemble of the src SH3 domain, and second, the features of the protein that determine its folding mechanism. Kinetic analysis of mutations at 52 of the 57 residues in the src SH3 domain revealed that the transition state ensemble is even more polarized than suspected earlier: no single alanine substitution in the N-terminal 15 residues or the C-terminal 9 residues has more than a two-fold effect on the folding rate, while such substitutions at 15 sites in the central three-stranded beta-sheet cause significant decreases in the folding rate. Molecular dynamics (MD) unfolding simulations and ab initio folding simulations on the src SH3 domain exhibit a hierarchy of folding similar to that observed in the experiments. The similarity in folding mechanism of different SH3 domains and the similar hierarchy of structure formation observed in the experiments and the simulations can be largely accounted for by a simple native state topology-based model of protein folding energy landscapes.

Robustness of protein folding kinetics to surface hydrophobic substitutions.

We use both combinatorial and site-directed mutagenesis to explore the consequences of surface hydrophobic substitutions for the folding of two small single domain proteins, the src SH3 domain, and the IgG binding domain of Peptostreptococcal protein L. We find that in almost every case, destabilizing surface hydrophobic substitutions have much larger effects on the rate of unfolding than on the rate of folding, suggesting that nonnative hydrophobic interactions do not significantly interfere with the rate of core assembly.

Important role of hydrogen bonds in the structurally polarized transition state for folding of the src SH3 domain.

Experimental and theoretical studies on the folding of small proteins such as the chymotrypsin inhibitor 2 (CI-2) and the P22 Arc repressor suggest that the folding transition state is an expanded version of the native state with most interactions partially formed. Here we report that this picture does not hold generally: a hydrogen bond network involving two beta-turns and an adjacent hydrophobic cluster appear to be formed in the folding transition state of the src SH3 domain, while the remainder of the polypeptide chain is largely unstructured. Comparison with data on other small proteins suggests that this structural polarization is a consequence of the topology of the SH3 domain fold. The non-uniform distribution of structure in the folding transition state provides a challenging test for computational models of the folding process.

Development of proliferative diabetic retinopathy in African-Americans and whites with type 1 diabetes.

OBJECTIVE: To investigate the comparable risk of developing proliferative diabetic retinopathy (PDR) in African-Americans and whites with type 1 diabetes. RESEARCH DESIGN AND METHODS: Using a cohort design with the sample drawn from medical records, the sample consisted of 312 people with type 1 diabetes (97 African-Americans, 215 whites) having at least two visits to a Model Demonstration Unit with gradeable fundus photographs (stereo, color, 7 standard fields). Excluded were subjects with preexisting or treated PDR or hemoglobinopathy. Masked grading of the fundus photographs was conducted at the Wisconsin Reading Center. RESULTS: At baseline, African-Americans had poorer glycemic control (mean HbA1 of 11.3 vs. 10.0%, P < 0.0001), higher systolic blood pressure (mean of 117 vs. 110 mmHg, P < 0.001), and were older (mean of 26.8 vs. 19.3 years, P < 0.0001) than the white subjects. African-Americans also tended to have slightly longer duration of diabetes and length of follow-up. In the African-Americans, 17.5% developed PDR, compared with 10.2% in the 215 whites, for an odds ratio (OR) of 1.86 (95% CI 0.93-3.70). When adjusted for baseline glycemic control, retinopathy grade, and length of follow-up, race was not a significant risk factor (OR = 0.73, 95% CI 0.30-1.78). CONCLUSIONS: African-Americans with type 1 diabetes may have a higher rate of developing PDR. The observed racial difference, however, is attributable to the presence of a worse risk factor profile, especially to poorer glycemic control. Efforts should be expanded to improve the care for all individuals with poor glycemic control.

Disparity in glycemic control and adherence between African-American and Caucasian youths with diabetes. Family and community contexts.

OBJECTIVE: To describe sociodemographic, family, and community factors that contribute to the glycemic control of African-American and Caucasian youths with diabetes, we investigated two questions: 1) Is there a disparity in glycemic control between African-American and Caucasian youths with diabetes, and if so, what sociodemographic, family, and community factors explain the disparity? and 2) Is there a difference in the adherence to treatment between African-American and Caucasian youths with diabetes, and if so, what sociodemographic, family, and community factors explain the difference? RESEARCH DESIGN AND METHODS: This cross-sectional study included 146 youths with diabetes (95 Caucasians and 51 African-Americans) and their mothers. The youths were invited to participate if they had been diagnosed with diabetes at least 1 year before the study, did not have another chronic illness, and were < 18 years of age. RESULTS: The findings indicate that African-American youths with diabetes are in significantly poorer metabolic control than their Caucasian counterparts (1.5% difference in HbA1c levels). Single-parent household status and lower levels of adherence partially account for the poorer glycemic control. Examination of the adherence subscales indicates that African-Americans report significantly lower adherence to diet and glucose testing than Caucasian youths. CONCLUSIONS: This study suggests that African-American youths with diabetes may be at greater risk for poor glycemic control due to the higher prevalence of single parenting and lower levels of adherence found in this population.

Functional rapidly folding proteins from simplified amino acid sequences.

Early protein synthesis is thought to have involved a reduced amino acid alphabet. What is the minimum number of amino acids that would have been needed to encode complex protein folds similar to those found in nature today? Here we show that a small beta-sheet protein, the SH3 domain, can be largely encoded by a five letter amino acid alphabet but not by a three letter alphabet. Furthermore, despite the dramatic changes in sequence, the folding rates of the reduced alphabet proteins are very close to that of the naturally occurring SH3 domain. This finding suggests that despite the vast size of the search space, the rapid folding of biological sequences to their native states is not the result of extensive evolutionary optimization. Instead, the results support the idea that the interactions which stabilize the native state induce a funnel shape to the free energy landscape sufficient to guide the folding polypeptide chain to the proper structure.

Pathophysiology of type 2 diabetes and modes of action of therapeutic interventions.

At least 90% of the 12 to 15 million persons with diabetes mellitus in the United States, half of whose condition remains undiagnosed, have type 2 diabetes. Type 2 diabetes is preceded by a long period of impaired glucose tolerance, a reversible metabolic state associated with increased prevalence of macrovascular complications. Thus, at the time of diagnosis, long-term complications have developed in almost one fourth of patients. Susceptibility to type 2 diabetes requires genetic (most likely polygenic) and acquired factors, and its pathogenesis involves an interplay of progressive insulin resistance and beta-cell failure. The ideal treatment of type 2 diabetes should reverse insulin resistance and beta-cell dysfunction in most treated patients and prevent, delay, or reverse long-term complications. Current strategies are aimed at amelioration of insulin resistance (diet, exercise, weight loss, and metformin and troglitazone therapy), augmentation of insulin supply (sulfonylurea and insulin therapy), or limitation of postprandial hyperglycemia (acarbose therapy). Future therapies probably will target (1) insulin resistance, using a multifaceted approach; (2) hepatic glucose production, using gluconeogenesis inhibitors; (3) excess nonesterified fatty acid production, using lipolysis inhibitors; and (4) fat oxidation, using carnitine palmitoyltransferase I and II inhibitors. Attempts also could be made to stimulate energy expenditure and increase nonoxidative glucose disposal by means of beta 3-adrenoceptor agonists. One promising strategy is an attack on multiple pathophysiological processes by combining antidiabetic agents with disparate mechanisms of action. Thus, we now have unprecedented resources for drug therapy for diabetes, with great opportunity for innovative combinations. It is hoped that these expanded choices will provide the tools necessary for a more efficient management of type 2 diabetes and prevention of its long-term complications.

Mothers' satisfaction with medical care: perceptions of racism, family stress, and medical outcomes in children with diabetes.

Patient satisfaction is an important indicator of medical outcomes. This study used an ecological framework to identify sociodemographic, family, and community predictors of mothers' satisfaction with their children's medical care and to determine the extent to which satisfaction is associated with medical outcomes such as adherence to treatment and health status of children with diabetes. Although individual demographics have little influence on satisfaction, family and community stressors are significant predictors of mothers' satisfaction with medical care. Mothers who reported greater perceptions of racism and family stress were significantly less satisfied with their children's medical care than those from less stressful environments. Mothers' satisfaction with medical care was significantly associated with adherence but was not significantly related to the children's health status.

Research on social support in adolescents with IDDM: a critical review.

This article provides a review of the findings of 32 scientific studies that examined the relationship between social support and adherence/metabolic control in adolescents with insulin-dependent diabetes mellitus. Social support included qualitative family support characteristics, communication patterns, sibling and peer relationships, and regimen-specific support behaviors. The literature was examined in the context of adolescent development. Although the results of these studies were somewhat inconsistent, some general patterns emerged that are described and discussed in detail. Methodological limitations and suggestions for future research are provided.

Serum leptin concentrations in human immunodeficiency virus-infected men with low adiposity.

The product of the obese gene (ob) is the protein leptin, which is synthesized in and secreted from adipocytes. Fasting serum leptin concentrations are closely related to body fat content and are higher in obese than in normal-weight individuals. Leptin may contribute to body weight regulation. Overproduction of leptin in certain pathologic conditions such as acquired immunodeficiency syndrome (AIDS) might in principle contribute to the low body fat content associated with body wasting. We measured fasting serum leptin levels by radioimmunoassay in individuals infected with the human immunodeficiency virus (HIV) and in a group of healthy lean men to determine whether HIV infection increases leptin levels. Thirteen HIV-infected men aged 26 to 50 years with a body mass index (BMI) of 15 to 26 kg/m2 and 4 to 24 kg body fat (7% to 29% body fat) had serum leptin levels (3.4 +/- 1.6 ng/mL) that were not elevated compared with the levels in 17 healthy men (4.0 +/- 1.4 ng/mL) matched for age (23 to 47 years), BMI (18 to 26 kg/m2), and body fat (5 to 21 kg; 9% to 28%). In both groups of men, serum leptin concentrations were correlated with percent body fat and body fat content (P < .001), and these relationships were not different between the two groups. In both groups, leptin concentrations were not correlated with lean body mass (P > or = .24). Energy intake in the HIV-infected men, assessed from 3-day intake records, was within the normal range. These findings extend the hypothesis that circulating leptin concentrations directly reflect adipose tissue mass, even in HIV-infected men with low body fat content. These findings do not support the hypothesis that HIV infection is associated with high circulating leptin concentrations, and suggest that low leptin levels do not stimulate food intake in HIV-infected individuals.

Increased plasma leptin concentration in end-stage renal disease.

Leptin is a 16-kDa protein recently identified as the obese gene product involved in body weight regulation. Administration of recombinant leptin to ob/ob mice, which have a genetic defect in leptin production, reduces food intake and increases energy expenditure. Leptin is synthesized by fat cells, and in normal humans, plasma concentrations are proportional to adiposity. The physiological actions and the degradation pathways of leptin in humans are unknown. We investigated renal elimination of leptin by comparing plasma leptin concentrations in end-stage renal disease (ESRD) patients with normal controls. Our hypothesis was that if renal filtration is a significant route of elimination, the hormone would accumulate in ESRD patients. Mean plasma levels in 141 ESRD patients (26.8 +/- 5.7 and 38.3 +/- 5.6 micrograms/L for males and females, respectively) were significantly higher (P < 0.001) than mean values obtained in normal controls (11.9 +/- 3.1 and 21.2 +/- 3.0 micrograms/L for males and females, respectively). Leptin concentrations in ESRD patients correlated directly with body mass index (BMI; r = 0.77 for men and 0.78 for women). The rate of increase in leptin concentrations with BMI was significantly greater in ESRD patients (5.5 and 6.6 micrograms/L/U BMI for men and women, respectively) than in normal controls (1.4 and 2.6 micrograms/L/U for men and women, respectively). Pre- and postdialysis leptin levels in hemodialysis patients were similar. Western blot of plasma from ESRD patients with high leptin levels showed bands corresponding to the intact protein (16 kDa) with no lesser or greater molecular mass species observed. Leptin concentrations in patients with ESRD did not correlate with measures of residual renal function (serum creatinine, beta 2-microglobulin, PTH, or GH levels). Similarly, we found no correlation between leptin levels and the number of years patients had been on dialysis or with recent weight changes. We conclude that intact leptin is increased in ESRD patients, but does not appear to cause decreased weight. As leptin levels did not correlate with residual renal function, increased production may account for the high levels observed.

New advances in insulin treatment of diabetes: overcoming barriers.

OBJECTIVE: To discuss the optimal role of insulin in the treatment of patients with diabetes mellitus. METHODS: We review the complications of diabetes, highlight the attempts to improve control of plasma glucose, and summarize current recommendations for use of insulin in clinical practice. RESULTS: With the strict new guidelines for the diagnosis of diabetes issued by the American Diabetes Association in July 1997--a plasma glucose level of 126 mg/dL (7 mmol/L) rather than 140 mg/dL (7.8 mmol/L)--an additional 8 million persons will be diagnosed this year, and diabetes and its complications will be at the forefront of public health concerns. Strong evidence indicates that with reduction of plasma glucose levels and tight control of glycohemoglobin, the rate of complications can be considerably decreased. Although insulin replacement therapy is well known to be both the best and the most cost-effective way to control glucose levels in patients with type 1 diabetes, studies have no shown that those with type 2 diabetes can likewise benefit from appropriate insulin therapy. Other investigations have indicated that coronary events are as likely to occur in patients with recently discovered impaired glucose tolerance as in patients with known diabetes (at a 2-hour postprandial glucose threshold of 96 mg/dL [5.3 mmol/L]). Such finding suggest that there may be no such thing as "borderline diabetes" and give impetus to the search for improved types of insulin to treat all patients with diabetes. A recent candidate is the new insulin analogue lispro, which was developed by recombinant DNA techniques, with its design influenced by the structural analogy to another endogenous hormone, insulin-like growth factor I. Lispro is a fast-acting, rapidly dissipating insulin formulation. This profile allows lispro to be given less than 15 minutes before a meal, yet with little risk of postprandial hypoglycemia because its high mealtime peak is followed by rapid disappearance from the bloodstream. CONCLUSION: Lispro has been shown to improve postprandial control of plasma glucose and to decrease the occurrence of hypoglycemia episodes in comparison with regular insulin. Because of its stability and pharmacokinetic properties, lispro can also be used in insulin pump therapy.

Radioimmunoassay of leptin in human plasma.

Recent studies suggest that leptin, the ob gene product absent in ob/ob mice, is a negative regulator of adiposity. We developed an RIA to measure human leptin in plasma or serum. The minimum detectable concentration by the assay is 0.5 microg/L leptin and the limit of linearity is 100 microg/L. Recovery of leptin added to serum was 99-104% over by the linear range of the assay. The RIA agreed reasonably well with rough quantification by Western blot (RIA = 0.90 blot + 3.7 microg/L, Sy/x = 10.9 microg/L). CVs within- and between-run ranged from 3.4% to 8.3% and from 3.6% to 6.2%, respectively. Variation in plasma leptin concentrations in specimens collected on consecutive mornings was large (CVs of 10.9% and 22.5%). After an overnight fast, leptin concentrations were similar to those 1-2 h after 1-2 meals. Plasma leptin concentrations in specimens from 83 lean and obese adults correlated directly with body mass index (BMI; kg/m2): r = 0.72, P <0.001. Correlations were significantly improved by separating results by gender (men r = 0.84, women r = 0.87; p <0.001). The increase in leptin concentrations with increasing BMI was greater in women than in men (slope 2.53 vs 0.97 microg/L per unit BMI, respectively). Leptin concentrations determined in lean subjects (BMI between 18 and 25) were higher in women (7.36 +/- 3.73 microg/L) than in men (3.84 +/- 1.79 microg/L) (P <0.001). Plasma leptin varied little with age and no significant difference was observed between whites and blacks. We conclude that: (a) plasma leptin concentrations are accurately and precisely measured by this new RIA; (b) leptin concentrations vary little due to short-term fasting, age, or race; but (c) plasma leptin concentrations are gender specific.

Major decrements in glycated hemoglobin levels between 1978 and 1989 in patients with insulin-dependent diabetes mellitus.

The Diabetes Control and Complications Trial has shown that intensive treatment can deter the development and progression of diabetic complications. Integral to intensive treatment is improved glycemic control. To describe the trend in glycemic control for subjects with insulin-dependent diabetes mellitus, we examined the medical records of 662 subjects seen between 1978 and 1989 at the Model Demonstration Unit of the Diabetes Research and Training Center (Washington University School of Medicine). Mean value of glycated hemoglobin showed steady decline from a peak of 11.5% in 1979 to 9.0% in 1989. This decline was observed both in subjects evaluated only once (annual rate of decline estimated from linear regression, -0.17 +/1 0.03; p = 0.0001) and in subjects evaluated more than once (annual rate of decline estimated from growth curves, -0.18 +/- 0.06; p = 0.0001). These results suggest that substantial lowering of glycated hemoglobin has occurred during the last decade. This reduction should result in a lowered risk of diabetic complications.