Native-state proteomics of Parvalbumin interneurons identifies unique molecular signatures and vulnerabilities to early Alzheimer's pathology

Dysfunction in fast-spiking parvalbumin interneurons (PV-INs) may represent an early pathophysiological perturbation in Alzheimer's Disease (AD). Defining early proteomic alterations in PV-INs can provide key biological and translationally-relevant insights. We used cell-type-specific in-vivo biotinylation of proteins (CIBOP) coupled with mass spectrometry to obtain native-state PV-IN proteomes. PV-IN proteomic signatures include high metabolic and translational activity, with over-representation of AD-risk and cognitive resilience-related proteins. In bulk proteomes, PV-IN proteins were associated with cognitive decline in humans, and with progressive neuropathology in humans and the 5xFAD mouse model of Aβ pathology. PV-IN CIBOP in early stages of Aβ pathology revealed signatures of increased mitochondria and metabolism, synaptic and cytoskeletal disruption and decreased mTOR signaling, not apparent in whole-brain proteomes. Furthermore, we demonstrated pre-synaptic defects in PV-to-excitatory neurotransmission, validating our proteomic findings. Overall, in this study we present native-state proteomes of PV-INs, revealing molecular insights into their unique roles in cognitive resiliency and AD pathogenesis.

Identification of State-Specific Proteomic and Transcriptomic Signatures of Microglia-Derived Extracellular Vesicles

Microglia are resident immune cells of the brain that play important roles in mediating inflammatory responses in several neurological diseases via direct and indirect mechanisms. One indirect mechanism may involve extracellular vesicle (EV) release, so that the molecular cargo transported by microglia-derived EVs can have functional effects by facilitating intercellular communication. The molecular composition of microglia-derived EVs, and how microglial activation states impact EV composition and EV-mediated effects in neuroinflammation, remain poorly understood. We hypothesize that microglia-derived EVs have unique molecular profiles that are determined by microglial activation state. Using size-exclusion chromatography to purify EVs from BV2 microglia, combined with proteomic (label-free quantitative mass spectrometry or LFQ-MS) and transcriptomic (mRNA and noncoding RNA seq) methods, we obtained comprehensive molecular profiles of microglia-derived EVs. LFQ-MS identified several classic EV proteins (tetraspanins, ESCRT machinery, and heat shock proteins), in addition to over 200 proteins not previously reported in the literature. Unique mRNA and microRNA signatures of microglia-derived EVs were also identified. After treating BV2 microglia with lipopolysaccharide (LPS), interleukin-10, or transforming growth factor beta, to mimic pro-inflammatory, anti-inflammatory, or homeostatic states, respectively, LFQ-MS and RNA seq revealed novel state-specific proteomic and transcriptomic signatures of microglia-derived EVs. Particularly, LPS treatment had the most profound impact on proteomic and transcriptomic compositions of microglia-derived EVs. Furthermore, we found that EVs derived from LPS-activated microglia were able to induce pro-inflammatory transcriptomic changes in resting responder microglia, confirming the ability of microglia-derived EVs to relay functionally relevant inflammatory signals. These comprehensive microglia-EV molecular datasets represent important resources for the neuroscience and omics communities and provide novel insights into the role of microglia-derived EVs in neuroinflammation.

Identification of state-specific proteomic and transcriptomic signatures of microglia-derived extracellular vesicles

Microglia are resident immune cells of the brain that play important roles in mediating inflammatory responses in several neurological diseases via direct and indirect mechanisms. One indirect mechanism may involve extracellular vesicle (EV) release, so that the molecular cargo transported by microglia-derived EVs can have functional effects by facilitating intercellular communication. The molecular composition of microglia-derived EVs, and how microglial activation states impacts EV composition and EV-mediated effects in neuroinflammation, remain poorly understood. We hypothesize that microglia-derived EVs have unique molecular profiles that are determined by microglial activation state. Using size-exclusion chromatography to purify EVs from BV2 microglia, combined with proteomic (label-free quantitative mass spectrometry or LFQ-MS) and transcriptomic (mRNA and non-coding RNA seq) methods, we obtained comprehensive molecular profiles of microglia-derived EVs. LFQ-MS identified several classic EV proteins (tetraspanins, ESCRT machinery, and heat shock proteins), in addition to over 200 proteins not previously reported in the literature. Unique mRNA and microRNA signatures of microglia-derived EVs were also identified. After treating BV2 microglia with lipopolysaccharide (LPS), interleukin-10, or transforming growth factor beta, to mimic pro-inflammatory, anti-inflammatory, or homeostatic states, respectively, LFQ-MS and RNA seq revealed novel state-specific proteomic and transcriptomic signatures of microglia-derived EVs. Particularly, LPS treatment had the most profound impact on proteomic and transcriptomic compositions of microglia-derived EVs. Furthermore, we found that EVs derived from LPS-activated microglia were able to induce pro-inflammatory transcriptomic changes in resting responder microglia, confirming the ability of microglia-derived EVs to relay functionally-relevant inflammatory signals. These comprehensive microglia-EV molecular datasets represent important resources for the neuroscience and glial communities, and provide novel insights into the role of microglia-derived EVs in neuroinflammation.

Advances in proteomic phenotyping of microglia in neurodegeneration

Microglia are dynamic resident immune cells of the central nervous system (CNS) that sense, survey, and respond to changes in their environment. In disease states, microglia transform from homeostatic to diverse molecular phenotypic states that play complex and causal roles in neurologic disease pathogenesis, as evidenced by the identification of microglial genes as genetic risk factors for neurodegenerative disease. While advances in transcriptomic profiling of microglia from the CNS of humans and animal models have provided transformative insights, the transcriptome is only modestly reflective of the proteome. Proteomic profiling of microglia is therefore more likely to provide functionally and therapeutically relevant targets. In this review, we discuss molecular insights gained from transcriptomic studies of microglia in the context of Alzheimer's disease as a prototypic neurodegenerative disease, and highlight existing and emerging approaches for proteomic profiling of microglia derived from in vivo model systems and human brain.

Native-state proteomics of Parvalbumin interneurons identifies novel molecular signatures and metabolic vulnerabilities to early Alzheimer's disease pathology

One of the earliest pathophysiological perturbations in Alzheimer's Disease (AD) may arise from dysfunction of fast-spiking parvalbumin (PV) interneurons (PV-INs). Defining early protein-level (proteomic) alterations in PV-INs can provide key biological and translationally relevant insights. Here, we use cell-type-specific in vivo biotinylation of proteins (CIBOP) coupled with mass spectrometry to obtain native-state proteomes of PV interneurons. PV-INs exhibited proteomic signatures of high metabolic, mitochondrial, and translational activity, with over-representation of causally linked AD genetic risk factors. Analyses of bulk brain proteomes indicated strong correlations between PV-IN proteins with cognitive decline in humans, and with progressive neuropathology in humans and mouse models of Aβ pathology. Furthermore, PV-IN-specific proteomes revealed unique signatures of increased mitochondrial and metabolic proteins, but decreased synaptic and mTOR signaling proteins in response to early Aβ pathology. PV-specific changes were not apparent in whole-brain proteomes. These findings showcase the first native state PV-IN proteomes in mammalian brain, revealing a molecular basis for their unique vulnerabilities in AD.

Intermittent Hypoxia Differentially Regulates Adenosine Receptors in Phrenic Motor Neurons with Spinal Cord Injury

Cervical spinal cord injury (cSCI) impairs neural drive to the respiratory muscles, causing life- threatening complications such as respiratory insufficiency and diminished airway protection. Repetitive "low dose" acute intermittent hypoxia (AIH) is a promising strategy to restore motor function in people with chronic SCI. Conversely, "high dose" chronic intermittent hypoxia (CIH; ∼8 h/night), such as experienced during sleep apnea, causes pathology. Sleep apnea, spinal ischemia, hypoxia and neuroinflammation associated with cSCI increase extracellular adenosine concentrations and activate spinal adenosine receptors which in turn constrains the functional benefits of therapeutic AIH. Adenosine 1 and 2A receptors (A₁, A_2A) compete to determine net cAMP signaling and likely the tAIH efficacy with chronic cSCI. Since cSCI and intermittent hypoxia may regulate adenosine receptor expression in phrenic motor neurons, we tested the hypotheses that: 1) daily AIH (28 days) downregulates A_2A and upregulates A₁ receptor expression; 2) CIH (28 days) upregulates A_2A and downregulates A₁ receptor expression; and 3) cSCI alters the impact of CIH on adenosine receptor expression. Daily AIH had no effect on either adenosine receptor in intact or injured rats. However, CIH exerted complex effects depending on injury status. Whereas CIH increased A₁ receptor expression in intact (not injured) rats, it increased A_2A receptor expression in spinally injured (not intact) rats. The differential impact of CIH reinforces the concept that the injured spinal cord behaves in distinct ways from intact spinal cords, and that these differences should be considered in the design of experiments and/or new treatments for chronic cSCI.

Brain Cell Type-Specific Nuclear Proteomics Is Imperative to Resolve Neurodegenerative Disease Mechanisms

Neurodegenerative diseases (NDs) involve complex cellular mechanisms that are incompletely understood. Emerging findings have revealed that disruption of nuclear processes play key roles in ND pathogenesis. The nucleus is a nexus for gene regulation and cellular processes that together, may underlie pathomechanisms of NDs. Furthermore, many genetic risk factors for NDs encode proteins that are either present in the nucleus or are involved in nuclear processes (for example, RNA binding proteins, epigenetic regulators, or nuclear-cytoplasmic transport proteins). While recent advances in nuclear transcriptomics have been significant, studies of the nuclear proteome in brain have been relatively limited. We propose that a comprehensive analysis of nuclear proteomic alterations of various brain cell types in NDs may provide novel biological and therapeutic insights. This may be feasible because emerging technical advances allow isolation and investigation of intact nuclei from post-mortem frozen human brain tissue with cell type-specific and single-cell resolution. Accordingly, nuclei of various brain cell types harbor unique protein markers which can be used to isolate cell-type specific nuclei followed by down-stream proteomics by mass spectrometry. Here we review the literature providing a rationale for investigating proteomic changes occurring in nuclei in NDs and then highlight the potential for brain cell type-specific nuclear proteomics to enhance our understanding of distinct cellular mechanisms that drive ND pathogenesis.

Cell type-specific biotin labeling in vivo resolves regional neuronal and astrocyte proteomic differences in mouse brain

Proteomic profiling of brain cell types using isolation-based strategies pose limitations in resolving cellular phenotypes representative of their native state. We describe a mouse line for cell type-specific expression of biotin ligase TurboID, for in vivo biotinylation of proteins. Using adenoviral and transgenic approaches to label neurons, we show robust protein biotinylation in neuronal soma and axons throughout the brain, allowing quantitation of over 2000 neuron-derived proteins spanning synaptic proteins, transporters, ion channels and disease-relevant druggable targets. Next, we contrast Camk2a-neuron and Aldh1l1-astrocyte proteomes and identify brain region-specific proteomic differences within both cell types, some of which might potentially underlie the selective vulnerability to neurological diseases. Leveraging the cellular specificity of proteomic labeling, we apply an antibody-based approach to uncover differences in neuron and astrocyte-derived signaling phospho-proteins and cytokines. This approach will facilitate the characterization of cell-type specific proteomes in a diverse number of tissues under both physiological and pathological states.

Identification of state-specific proteomic characteristics of microglia-derived exosomes

BACKGROUND

Alzheimer's disease (AD) is the most common neurodegenerative disorder defined by progressive pathological protein aggregation (amyloid-beta and tau) and deterioration of cognitive function. Microglia-mediated neuroinflammation is a key pathological component of AD; however, there are critical gaps in our understanding of how microglia perpetuate AD pathology. One proposed mechanism of microglia-mediated neuroinflammation and neurodegeneration is exosome release because of their critical role in the transport of macromolecules between cells to facilitate intercellular communication. Thus, it is possible that microglia-derived exosomes transfer pathogenic cargo which could perpetuate AD pathology. The proteomic profiles and influence of different microglia-derived exosomal populations on AD pathology remain unknown. We hypothesize that different microglia states determine the molecular composition of exosomes.

METHOD

We treated a murine microglia cell line, BV2 cells, with various cytokines to polarize them and collect their exosomes for downstream mass spectrometry (MS) analyses. Three groups of BV2 cells (n=4/group) were treated with either lipopolysaccharide (LPS) to polarize to a pro-inflammatory state, interleukin 10 (IL-10) to polarize to an anti-inflammatory state, or transforming growth factor beta (TGF-β) to polarize to a homeostatic state. Untreated BV2 cells served as a control group. Following 72 hours of treatment, BV2 cells were lysed and cell culture media was collected for exosome isolation.

RESULT

Transmission electron microscopy images and western blotting for exosomal marker, CD9, confirmed exosome purification by our isolation method. In MS studies, we identified 533 proteins in exosome fractions and 1,866 proteins in BV2 cell proteomes. We found that known exosome related proteins, Sdcbp and Igsf8, were significantly increased in the exosomal proteome compared to the whole cell proteome. We identified proteins that are differentially expressed across polarization with unique proteins increased in exosomes derived from LPS, IL-10, and TGF-β treated BV2 cells. Validation studies of these top hits are ongoing, and studies are underway to replicate these findings in primary microglia.

CONCLUSION

Our results indicate that exosomes derived from microglia adopt distinct state-associated protein profiles which may have differential effects on other cell types. This work will guide future studies concerning the role of exosomal cargo in perpetuating AD pathology.

Phrenic motor neuron survival below cervical spinal cord hemisection

Cervical spinal cord injury (cSCI) severs bulbospinal projections to respiratory motor neurons, paralyzing respiratory muscles below the injury. C2 spinal hemisection (C2Hx) is a model of cSCI often used to study spontaneous and induced plasticity and breathing recovery post-injury. One key assumption is that C2Hx dennervates motor neurons below the injury, but does not affect their survival. However, a recent study reported substantial bilateral motor neuron death caudal to C2Hx. Since phrenic motor neuron (PMN) death following C2Hx would have profound implications for therapeutic strategies designed to target spared neural circuits, we tested the hypothesis that C2Hx minimally impacts PMN survival. Using improved retrograde tracing methods, we observed no loss of PMNs at 2- or 8-weeks post-C2Hx. We also observed no injury-related differences in ChAT or NeuN immunolabeling within labelled PMNs. Although we found no evidence of PMN loss following C2Hx, we cannot rule out neuronal loss in other motor pools. These findings address an essential prerequisite for studies that utilize C2Hx as a model to explore strategies for inducing plasticity and/or regeneration within the phrenic motor system, as they provide important insights into the viability of phrenic motor neurons as therapeutic targets after high cervical injury.

Serotonergic innervation of respiratory motor nuclei after cervical spinal injury: Impact of intermittent hypoxia

Although cervical spinal cord injury (cSCI) disrupts bulbo-spinal serotonergic projections, partial recovery of spinal serotonergic innervation below the injury site is observed after incomplete cSCI. Since serotonin contributes to functional recovery post-injury, treatments to restore or accelerate serotonergic reinnervation are of considerable interest. Intermittent hypoxia (IH) was reported to increase serotonin innervation near respiratory motor neurons in spinal intact rats, and to improve function after cSCI. Here, we tested the hypotheses that spontaneous serotonergic reinnervation of key respiratory (phrenic and intercostal) motor nuclei: 1) is partially restored 12 weeks post C2 hemisection (C2Hx); 2) is enhanced by IH; and 3) results from sprouting of spared crossed-spinal serotonergic projections below the site of injury. Serotonin was assessed via immunofluorescence in male Sprague Dawley rats with and without C2Hx (12 wks post-injury); individual groups were exposed to 28 days of: 1) normoxia; 2) daily acute IH (dAIH28: 10, 5 min 10.5% O2 episodes per day; 5 min normoxic intervals); 3) mild chronic IH (IH28-5/5: 5 min 10.5% O2 episodes; 5 min intervals; 8 h/day); or 4) moderate chronic IH (IH28-2/2: 2 min 10.5% O2 episodes; 2 min intervals; 8 h/day), simulating IH experienced during moderate sleep apnea. After C2Hx, the number of ipsilateral serotonergic structures was decreased in both motor nuclei, regardless of IH protocol. However, serotonergic structures were larger after C2Hx in both motor nuclei, and total serotonin immunolabeling area was increased in the phrenic motor nucleus but reduced in the intercostal motor nucleus. Both chronic IH protocols increased serotonin structure size and total area in the phrenic motor nuclei of uninjured rats, but had no detectable effects after C2Hx. Although the functional implications of fewer but larger serotonergic structures are unclear, we confirm that serotonergic reinnervation is substantial following injury, but IH does not affect the extent of reinnervation.

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.

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.

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.

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.

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.

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.

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.

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 &lt;0.001. Correlations were significantly improved by separating results by gender (men r = 0.84, women r = 0.87; p &lt;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 &lt;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.

I get by with a little help from my family and friends: adolescents' support for diabetes care

Evaluated and compared the support provided by family members and friends for adolescents' diabetes care. Family and friend support also were examined in relation to other measures of social support, to demographic variables (age, gender, duration of diabetes) and to adherence. Using a structured interview, 74 adolescents with diabetes described the ways that family members and friends provided support for diabetes management (insulin shots, blood glucose monitoring, eating proper meals, exercise), and for helping them to "feel good about their diabetes." Families provided more support than friends for three management tasks (insulin injections, blood glucose monitoring, meals); this support was largely instrumental. In contrast, friends provided more emotional support for diabetes than families. Greater family support was related to younger age, shorter disease duration, and better treatment adherence. Implications of the findings include encouraging parents to remain involved in adolescents' treatment management, and involving peers as supportive companions for meals and exercise.

Retinopathy in African Americans and whites with insulin-dependent diabetes mellitus

BACKGROUND

The development and progression of diabetic retinopathy in African Americans with insulin-dependent diabetes mellitus is not known.

METHODS

Two hundred subjects with insulin-dependent diabetes mellitus with duration of diabetes 16 years or less at first visit were studied; 58 were African Americans and 142 were whites. All had gradable stereoscopic color fundus photographs (seven standard fields) from at least two visits (mean time between first and second visit was 4.1 years). Subjects with hemoglobinopathy or proliferative retinopathy or subjects who had evidence of treatment for proliferative retinopathy at first visit were excluded. Masked grading of photographs was conducted using the modified Airlie House classification scheme.

RESULTS

African Americans were older, heavier, had higher systolic blood pressure (all P < .05), and marginally higher hemoglobin A1 (HbA1) values (P = .06) than the whites at first visit. African Americans had a lower rate of two steps or more progression from preexistent retinopathy (19%) than whites (43%). Progression to proliferative retinopathy or treatment was similar by race. Multivariate analysis predicting development oe progression of retinopathy, while controlling for length of follow-up, found higher HbA1 (odds ratio [OR] = 2.15), longer duration of insulin-dependent diabetes mellitus (OR = 1.69), higher serum creatinine concentration (OR = 1.59), and white race (OR = 2.62) to be independent risk factors.

CONCLUSIONS

These data suggest a previously unsuspected reduction in the adjusted risk for development and progression of retinopathy in African Americans. The reason for this apparently reduced risk are not known.

The relationship between eating patterns and metabolic control in patients with non-insulin-dependent diabetes mellitus (NIDDM)

The most important element in the therapeutic plan of patients with non-insulin-dependent diabetes mellitus (NIDDM) is dietary modification. Dietary instructions target patient behaviors in two areas: following an exchange-based diet and adhering to the same basic eating pattern every day. However, there is little empirical data that addresses the relationship between dietary instruction and metabolic control. Fifty patients with NIDDM were enrolled in an 8-week study to ascertain if either dietary approach was more predictive of improved metabolic control. The effect on metabolic control was determined by changes in HbA1c over a 2- to 3-month period. Patients added or deleted almost half of all prescribed exchanges, and added or deleted an average of one prescribed meal or snack per day. Deviations in prescribed eating patterns, particularly breakfast-skipping and snack additions and deletions, were related to poorer metabolic control. Maintaining consistent eating patterns should be further evaluated as an important component of dietary instruction for patients with NIDDM.

Potential autoantigens in IDDM. Expression of carboxypeptidase-H and insulin but not glutamate decarboxylase on the beta-cell surface

Insulin, carboxypeptidase-H (CP-H), and glutamate decarboxylase (GAD) have been identified as potential autoantigens in insulin-dependent diabetes mellitus (IDDM). Previous studies have described immunoreactive insulin as a surface molecule on the plasma membrane of rat islet cells and suggested that cell-surface insulin was derived during exocytosis by the fusion of insulin secretory granules with the beta-cell plasma membrane. These findings predict that insulin and other secretory granule-derived proteins such as the putative autoantigen CP-H may be colocalized with insulin at specific sites of exocytosis on the beta-cell surface. In studies to test this hypothesis, cell-surface staining of dispersed rat islet cells occurred in a granule-like pattern with antibodies for CP-H and insulin. The specificity of the CP-H antiserum was confirmed by immunoblotting and indicated that the antiserum was essentially monospecific for CP-H. Confocal laser microscopy confirmed that immunoreactive staining for CP-H and insulin was confined to the beta-cell surface. Colocalization of CP-H and insulin on the cell surface of beta-cells was demonstrated by double staining with antibodies to CP-H and insulin, and the percentage of beta-cells positive for both of these autoantigens increased twofold with increases in insulin secretion. In contrast, islet cells failed to reveal cell-surface staining for GAD65, another putative autoantigen in IDDM, under either basal or insulin stimulatory conditions or following exposure of islet cells to the cytokines interleukin-1 beta, tumor necrosis factor-alpha, and recombinant human interferon-gamma.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of the carbohydrase inhibitor miglitol in sulfonylurea-treated NIDDM patients

OBJECTIVE

To examine the effects of the carbohydrase inhibitor miglitol (BAY m 1099) on the metabolic profiles of non-insulin-dependent diabetes mellitus (NIDDM) patients suboptimally controlled on maximal daily doses of sulfonylurea (SFU) agents.

RESEARCH DESIGN AND METHODS

Multicenter, double-blind, randomized, placebo-controlled 14-week clinical trial with six-week, single-blind placebo lead-in and run-out periods. NIDDM volunteers (192) with fasting plasma glucose (FPG) 140-250 mg/dl and hemoglobin A1c (HbA1c) 6.5-12.0% after at least 4 weeks of treatment with SFU at maximal dose were stratified by baseline HbA1c (above and below 9.0%) and then randomly assigned within strata to placebo (n = 63), 50 mg miglitol 3 times a day (n = 61), or 100 mg miglitol 3 times a day (n = 68). Efficacy was assessed by HbA1c, FPG, insulin, and lipid concentrations, and by plasma glucose and serum insulin responses to a standard meal.

RESULTS

In the 50 and 100 mg miglitol treatment groups, the mean changes from baseline in HbA1c (with placebo values subtracted) were 0.82 and 0.74%, respectively, and were highly significant (P = 0.0001 in each case). Mean peak plasma glucose levels after a standard test meal were comparably lowered by 57 mg/dl with the 50 mg miglitol dose, and by 64 mg/dl with the 100 mg miglitol dose compared with placebo (P = 0.0001 for each), with associated reductions in integrated serum insulin response (P < 0.05). No significant drug-associated changes in FPG, insulin, or cholesterol levels were noted, but fasting triglyceride levels were lowered significantly with the 50 mg miglitol dose. Miglitol's side effects were limited to flatulence, loose stools, and abdominal discomfort, which were dose-related, rapidly resolved on drug discontinuation, and led to withdrawal from the study of 5 and 15% of patients taking 50 and 100 mg miglitol, respectively.

CONCLUSIONS

Miglitol may be indicated as effective adjuvant therapy in NIDDM patients with suboptimal metabolic control despite conventional treatment with diet and maximal daily doses of SFU. The dose of 50 mg miglitol 3 times a day may be preferable to 100 mg miglitol 3 times a day because of comparable efficacy and substantially reduced side effects.

D-chiro-inositol metabolism in diabetes mellitus

D-chiro-inositol is a rare inositol isomer present in inositol phosphoglycans which are proposed mediators of insulin action. To study D-chiro-inositol metabolism in diabetes mellitus, a sensitive and specific assay was developed using negative-ion chemical ionization gas chromatography/mass spectrometry. Median urinary D-chiro-inositol excretion, which was 2.1 mumol/day in nondiabetics, was substantially increased to 12 mumol/day in non-insulin-dependent diabetes (P < 0.0001) and to 74 mumol/day in insulin-dependent diabetes (P < 0.0001). Urinary D-chiro-inositol was strongly correlated with fasting plasma glucose (r = 0.568, P < 0.0001), glycated hemoglobin (r = 0.529, P < 0.0001), and urinary glucose (r = 0.368, P = 0.01). The renal clearance of D-chiro-inositol was selectively elevated in both non-insulin-dependent and insulin-dependent diabetes when compared with the clearances of L-chiro-inositol or myo-inositol and exceeded the glomerular filtration rate in 71% of the diabetics but in none of the nondiabetics. In poorly controlled diabetic patients insulin treatment reduced urinary D-chiro-inositol losses by 63% and increased plasma levels by 8.8-fold. The metabolism of D-chiro-inositol is abnormal in diabetes and appears to be influenced by short- and long-term metabolic control.

The relationship among six psychosocial domains, age, health care adherence, and metabolic control in adolescents with IDDM

This pilot study examined the relationship among six psychosocial factors, age, health care compliance, and metabolic control in adolescents with IDDM. Four objectives were identified: 1) to determine whether specific compliance areas predict metabolic control; 2) to determine whether specific psychosocial factors predict metabolic control; 3) to determine whether compliance and psychosocial issues change with age; and 4) to determine whether the parent or the youth is the more accurate predictor of metabolic control. Twenty-one adolescents age 13 through 18 years participated in this study. Dietary compliance was found to be the best predictor of metabolic control. Parents more accurately predicted metabolic control for youths younger than 16 years old, while the reverse was true for older youths. A negative relationship was identified among strong self-concept, high knowledge of IDDM, parental support, and poor metabolic control. Several possible explanations are discussed, including power struggles, coping difficulties, and fear of peer reactions.

Withdrawal of the aldose reductase inhibitor tolrestat in patients with diabetic neuropathy: effect on nerve function. The Tolrestat Study Group

A double-blind, placebo-controlled clinical trial was conducted to study the effects of discontinuing tolrestat, an aldose reductase inhibitor, on peripheral sensorimotor diabetic neuropathy. After an average of 4.2 years of continuous tolrestat use, 372 patients were randomly assigned to either placebo or continued tolrestat therapy and were followed for 52 weeks. After 3 months, patients who perceived worsening of symptoms of neuropathy were allowed to switch once to the alternate treatment group while maintaining the double-blind. Patients assigned to placebo had significant deterioration in motor nerve conduction velocity (MNCV) while those maintained on tolrestat did not (p < 0.05). The 28 patients who were randomly assigned to tolrestat and elected to switch to placebo had a significant deterioration in MNCV while the 36 assigned to placebo who switched to tolrestat had a significant improvement (p < 0.05). Treatment differences in favor of tolrestat were observed for sensation in the toes as well as for pain (p < 0.05). These data indicate that withdrawal from long-term treatment with tolrestat has a detrimental effect on several measures of diabetic neuropathy, whereas continuation of treatment is associated with stabilization of these measures, suggesting a continued role for polyol pathway activity in late neuropathy.

Family stress and resources: potential areas of intervention in children recently diagnosed with diabetes

This article examines the relationships among family stress, family capabilities, and the health status of 53 children diagnosed with insulin-dependent diabetes mellitus. Assessments were done at an outpatient diabetes clinic of family coping, resources, and stress; disease-related knowledge; metabolic control (HbA1); and endogenous insulin (C peptide). Results indicated that higher levels of family stress and lower levels of family resources as reported by fathers were significantly associated with poor metabolic control. Multiple regression analyses revealed that levels of family stress and resources were more strongly related to metabolic control than were disease variables such as C peptide levels. Moreover, family stress was directly associated with metabolic control, and family resources showed indirect linkages. Findings suggest that family stress and resources are potential areas for social work intervention in children recently diagnosed with diabetes.

Abnormal myocardial acoustic properties in diabetic patients and their correlation with the severity of disease

Although patients with diabetes mellitus may be afflicted by cardiomyopathy, its prevalence and nature are controversial. Studies have shown that fibrosis alters the acoustic properties of the heart in animals and humans and that the changes are detectable by cardiac tissue characterization with ultrasound. The present study was performed to characterize myocardial acoustic properties in patients with insulin-dependent diabetes to determine whether ultrasound tissue characterization could detect changes potentially indicative of occult cardiomyopathy. The magnitude of cyclic variation of myocardial ultrasound integrated backscatter and its phase delay with respect to the onset of the cardiac cycle in the septum and posterior wall of the left ventricle were measured in 54 patients with diabetes who had no overt cardiac disease. Conventional echocardiography documented normal ventricular systolic function in 96%. As compared with results in age-matched patients without diabetes studied previously, cyclic variation of integrated backscatter was reduced (4.6 +/- 0.8 vs. 3.6 +/- 1.4 dB; p less than 0.001). In addition, delay was significantly increased (0.86 +/- 0.09 vs. 0.99 +/- 0.15). The primary analysis of the data focused on differences among the diabetic patients. Reduction of cyclic variation of backscatter was greatest in patients with diabetes who had neuropathy (3.2 +/- 1.0 dB; p less than 0.001) as was the increase in delay (1.04 +/- 0.16, p less than 0.001 vs. values in patients without neuropathy). Retinopathy and nephropathy were associated with abnormal myocardial acoustic properties as well. Thus, abnormalities that may reflect fibrosis or other occult cardiomyopathic changes in diabetic patients without overt heart disease are readily detectable by myocardial tissue characterization with ultrasound and parallel the severity of noncardiac diabetic complications.

Effects of cyclosporine on insulin secretion and insulin sensitivity in dogs with intrasplenic islet autotransplants

Concern about cyclosporine causing adverse effects on glucose metabolism is based mainly on in vitro studies and in vivo data in rodents. However, data on large mammals and humans are much more controversial. Because the drug is used as therapy accompanying pancreatic or isolated islet transplantations, studies in large animals are needed to assess whether cyclosporine inhibits beta-cell function and causes glucose intolerance. To address these issues, we examined intravenous glucose tolerance, islet beta-cell function, and insulin sensitivity in a group of adult mongrel dogs with intrasplenic islet autografts, with and without cyclosporine treatment. Similar fasting plasma glucose and insulin values were found before and after pancreatectomy and islet transplantation. After intravenous glucose, plasma glucose values decreased more slowly in dogs that had undergone transplantation, but no additional adverse effect as a result of cyclosporine was observed. During euglycemic clamp studies, performed at both physiologic and pharmacologic insulin concentrations, the drug had no effect on the total amount of metabolized glucose, and glucose production was unaffected by cyclosporine treatment. Thus intramuscular cyclosporine therapy does not seem to inhibit insulin secretion from heterotopic islets or to affect peripheral and hepatic insulin sensitivity in dogs with intrasplenic islet autografts.

Absence of the dawn phenomenon and abnormal lipolysis in type 1 (insulin-dependent) diabetic patients with chronic growth hormone deficiency

To determine the role of growth hormone in overnight insulin requirements and lipolysis, five patients with chronic growth hormone deficiency and Type 1 (insulin-dependent) diabetes mellitus and six control patients with diabetes were each studied on two separate nights. Insulin was infused at a variable rate throughout one night to maintain euglycaemia and fixed at 04.00 hours on another. During the variable infusion, euglycaemia was maintained in control patients by a 36% increase in insulin infusion rate between 03.00 and 08.00 hours while a 46% decrease in the rate was required in growth hormone deficient patients (p less than 0.02). Despite this difference, mean free insulin values were equivalent. This finding is suggestive of increased insulin clearance in growth hormone sufficient patients. Glucose levels rose in control and fell in growth hormone deficient patients when insulin infusion rates were fixed at 04.00 hours. Glycerol production and non-esterified fatty acid concentrations were significantly lower in the growth hormone deficient diabetic patients, p less than 0.001, and when normalized with a heparin infusion, had no effect on insulin requirements. We conclude that: (1) growth hormone contributes to the development of the "dawn phenomenon," possibly by increasing insulin clearance (2) growth hormone helps sustain nocturnal lipolysis in Type 1 diabetes and (3) non-esterified fatty acids are not involved in the dawn phenomenon.