Are fewer cases of diabetes mellitus diagnosed in the months after SARS-CoV-2 infection? A population-level view in the EHR-based RECOVER program

Long-term sequelae of severe acute respiratory coronavirus-2 (SARS-CoV-2) infection may include increased incidence of diabetes. Here we describe the temporal relationship between new type 2 diabetes and SARS-CoV-2 infection in a nationwide database. We found that while the proportion of newly diagnosed type 2 diabetes increased during the acute period of SARS-CoV-2 infection, the mean proportion of new diabetes cases in the 6 months post-infection was about 83% lower than the 6 months preinfection. These results underscore the need for further investigation to understand the timing of new diabetes after COVID-19, etiology, screening, and treatment strategies.

Are fewer cases of diabetes mellitus diagnosed in the months after SARS-CoV-2 infection?

Long-term sequelae of severe acute respiratory coronavirus-2 (SARS-CoV-2) infection may include an increased incidence of diabetes. Our objective was to describe the temporal relationship between new diagnoses of diabetes mellitus and SARS-CoV-2 infection in a nationally representative database. There appears to be a sharp increase in diabetes diagnoses in the 30 days surrounding SARS-CoV-2 infection, followed by a decrease in new diagnoses in the post-acute period, up to 360 days after infection. These results underscore the need for further investigation, as understanding the timing of new diabetes onset after COVID-19 has implications regarding potential etiology and screening and treatment strategies.

Understanding heterogeneity of responses to, and optimizing clinical efficacy of, exercise training in older adults: NIH NIA Workshop summary

Exercise is a cornerstone of preventive medicine and a promising strategy to intervene on the biology of aging. Variation in the response to exercise is a widely accepted concept that dates back to the 1980s with classic genetic studies identifying sequence variations as modifiers of the VO₂max response to training. Since that time, the literature of exercise response variance has been populated with retrospective analyses of existing datasets that are limited by a lack of statistical power from technical error of the measurements and small sample sizes, as well as diffuse outcomes, very few of which have included older adults. Prospective studies that are appropriately designed to interrogate exercise response variation in key outcomes identified a priori and inclusive of individuals over the age of 70 are long overdue. Understanding the underlying intrinsic (e.g., genetics and epigenetics) and extrinsic (e.g., medication use, diet, chronic disease) factors that determine robust versus poor responses to various exercise factors will be used to improve exercise prescription to target the pillars of aging and optimize the clinical efficacy of exercise training in older adults. This review summarizes the proceedings of the NIA-sponsored workshop entitled, "Understanding Heterogeneity of Responses to, and Optimizing Clinical Efficacy of, Exercise Training in Older Adults" and highlights the importance and current state of exercise response variation research, particularly in older adults, prevailing challenges, and future directions.

Abstract P271: Delineating Sex-specific Mechanisms Of Impaired Vasoreactivity In Thermoneutrality

Cardiovascular disease (CVD) is a leading cause of hospitalization and death. CVD is characterized by impaired vasoreactivity and mitochondrial dysfunction. Perivascular adipose tissue (PVAT), considered brown adipose tissue (BAT), surrounds the vasculature and regulates its response. Preliminary data with rats housed at either their thermoneutrality (TN, 30°C) or room temperature (RT, 22°C) showed diminished vasodilation in aorta from TN rats as compared with those from RT rats (10.2% ± 4.0% (0.159 g of vasodilation capacity, starting from maximal force constriction of 1.563 g) versus 64.2% ± 5.3% (0.909 g of 1.417 g, p<0.001). TN-housed rat aorta also showed less mitochondrial respiration with lipid substrates in multiple states (p<0.05). We hypothesize that remodeling of PVAT phenotype from BAT to white adipose tissue (WAT) may alter mitochondrial lipid utilization and cause vasoreactivity dysfunction. To test this, we housed male and female rats at either RT or TN and investigated their own PVAT + aorta or PVAT from the oppositely- housed animals along with each rat’s own aorta for vasoreactivity ex situ. There was diminished vasodilation in all TN animals with PVAT + aorta (29.2% ± 3.8% (0.269 g of 0.923 g) versus 37.6% ± 6.0% (0.255 g of 0.677 g), p<0.02), with only male animals showing a significant effect from PVAT (p<0.001). In aorta of TN-housed animals analyzed with PVAT from RT-housed animals, female vessels showed an increase in vasodilation capacity as compared to controls (56.8% ± 13.6% (0.589 g of 1.037 g) versus 5.2% ± 2.3% (0.028 g of 0.534 g), p<0.001), strongly suggesting that PVAT not only regulates vasoreactivity, but can repair TN-induced diminished dilation in a sex-dependent manner. All animals at TN had significantly less mitochondrial respiration with lipid substrates (p<0.05), with no sex differences. We further observed a significantly greater amount of lipids in PVAT from male TN-housed animals as compared to that in RT-housed animals (p<0.05), consistent with a WAT phenotype. Our data support that TN alters PVAT phenotype in a sex-dependent manner, resulting in dysfunctional vasoreactivity and mitochondrial function. These targets of CVD in both male and female animals are exciting avenues for novel therapeutics.

SAT-670 The Perfect Storm for Diabetic Ketoacidosis

Background

Diabetic Ketoacidosis (DKA) is a life-threatening endocrine emergency characterized by metabolic acidosis occurring in the setting of hyperglycemia due to relative insulin deficiency leading to lipolysis and production of serum ketones. Clinical circumstances can potentiate this process, such as acute infection or insulin discontinuation. Additionally, patients on SGLT2-inhibitors are at risk for euglycemic DKA. In people with type 2 diabetes, DKA is uncommon; however, a combination of precipitating factors in these patients can lead to a greater risk of DKA, particularly in the setting of SGLT2-inhibitor use.

Clinical Case

A 63 year old male with past medical history significant for uncontrolled type 2 diabetes (10 year duration, HgA1c=11.2%, on insulins detemir and aspart, metformin, and empagliflozin), coronary artery disease, and treatment refractory antibody-negative polymyositis (baseline CPK levels ~1000-2000, on a burst of prednisone for flare) presented with fever (101.2F), fatigue, myalgias, and nausea with poor oral intake and insulin cessation after recent IV zoledronic acid infusion for prevention of steroid-induced osteoporosis. He was found to be acidemic with bicarbonate=16, AG=18, Cr=1.6 (baseline 1.1), lactic acid=2.9, glucose=245, glucosuria/ketonuria, serum osmolality=295, and CPK=3613. No infectious etiology was found. Differential diagnosis of precipitating factors of DKA includes: steroid-induced hyperglycemia with lipolysis and insulin resistance; starvation ketosis from poor oral intake due to bisphosphonate-induced flu-like illness; metformin-associated lactic acidosis in setting of acute kidney injury; ketone production secondary to insulin cessation in setting of febrile illness; and SGLT2-inhibitor use with dehydration secondary to decompensated hyperglycemia. He was treated for DKA with insulin and volume resuscitation. He was discharged with discontinuation of empagliflozin.

Conclusion

In people with type 2 diabetes and multiple medical problems, a collusion of clinical factors leading to acidemia can occur simultaneously and lead to a drastically increased risk of DKA, especially in the setting of SGLT2-inhibitor use. Clinicians should have heightened awareness of minor predisposing factors that in combination can increase risk of DKA in a patient with type 2 diabetes.

Peripheral insulin resistance in obese girls with hyperandrogenism is related to oxidative phosphorylation and elevated serum free fatty acids

Hyperandrogenic syndrome (HAS) is associated with insulin resistance (IR) and type 2 diabetes. Muscle IR in type 2 diabetes is linked with defects in mitochondrial oxidative capacity. In vivo muscle mitochondrial function has not been studied in HAS, especially in youth, who are early in the disease process. Our goal was to measure muscle mitochondrial oxidative function and peripheral IR in obese youth with HAS. Obese girls without HAS [n = 22, age 15(13,17) yr, BMI Z-score 2.05 ± 0.37] and with HAS [n = 35, age 15(14,16) yr, BMI Z-score 2.18 ± 0.30] were enrolled. Mitochondrial function was assessed with (31)phosphorus MR spectroscopy before, during, and after near-maximal isometric calf exercise, and peripheral IR was assessed with an 80 mU·m(-2)·min(-1) hyperinsulinemic euglycemic clamp. Girls with HAS had higher androgens [free androgen index 7.9(6.6,15.5) vs. 3.5(3.0,4.0), P < 0.01] and more IR [glucose infusion rate 9.4(7.0, 12,2) vs. 14.5(13.2,15.8) mg·kg lean(-1)·min(-1), P < 0.01]. HAS girls also had increased markers of inflammation including CRP, platelets, and white blood cell count and higher serum free fatty acids during hyperinsulinemia. Mitochondrial oxidative phosphorylation was lower in HAS [0.11(0.06,0.19) vs. 0.18(0.12,0.23) mmol/s, P < 0.05], although other spectroscopy markers of mitochondrial function were similar between groups. In multivariate analysis of the entire cohort, IR related to androgens, oxidative phosphorylation, and free fatty acid concentrations during hyperinsulinemia. These relationships were present in just the HAS cohort as well. Obese girls with HAS have significant peripheral IR, which is related to elevated androgens and free fatty acids and decreased mitochondrial oxidative phosphorylation. These may provide future options as targets for therapeutic intervention.

Renal function is associated with peak exercise capacity in adolescents with type 1 diabetes

OBJECTIVE

Diabetic nephropathy and cardiovascular disease are strongly related in adults with type 1 diabetes, yet little is known about this relationship in adolescents prior to the onset of detectable clinical disease. We hypothesized that cardiopulmonary fitness would be directly associated with albumin-to-creatinine ratio (ACR) and inversely related to estimated glomerular filtration rate (eGFR) in adolescents with type 1 diabetes.

RESEARCH DESIGN AND METHODS

Sixty-nine adolescents with type 1 diabetes and 13 nondiabetic control subjects of similar pubertal stage and BMI had insulin sensitivity (glucose infusion rate [GIR]), measured by hyperinsulinemic-euglycemic clamp, and lean body mass, measured by DEXA. Cardiopulmonary fitness was measured by cycle ergometry to obtain peak volume of oxygen (VO2peak), and renal function was measured by eGFR using the Bouvet equation (measuring creatinine and cystatin C levels) and ACR.

RESULTS

Adolescents (15.5 ± 2.2 years of age) with type 1 diabetes (6.3 ± 3.8 years diabetes duration) had reduced VO2peak (31.5 ± 6.3 vs. 36.2 ± 7.9 mL/kg ⋅ min, P = 0.046) and VO2peak/lean kg (43.7 ± 7.0 vs. 51.0 ± 8.6 mL/lean kg ⋅ min, P = 0.007) compared with nondiabetic control subjects. eGFR was inversely associated with VO2peak and VO2peak/lean kg after adjusting for sex, Tanner stage, GIR, HbA1c level, systolic blood pressure, and LDL cholesterol level (β ± SE, VO2peak: -0.19 ± 0.07, P = 0.02; VO2peak/lean kg: -0.19 ± 0.09, P = 0.048). Moreover, participants in the highest tertile for eGFR had significantly lower sex- and Tanner-adjusted VO2peak and VO2peak/lean kg compared with participants in the lowest tertile.

CONCLUSIONS

Adolescents with type 1 diabetes had reduced exercise capacity, which was strongly associated with renal health, independent of insulin sensitivity. Future studies should examine the underlying interrelated pathophysiology in order to identify probable targets for treatment to reduce cardiovascular and renal complications.

Abstract 523: Persistent Disrupted Mitochondrial Adaptation in Primary Vascular Cells from a Diabetic Model

People with diabetes (DM) have an excess burden of cardiovascular disease (CVD). Impairments in vascular contractility predict poor CVD outcomes, and mitochondria are essential for arterial contraction and relaxation. Mitochondrial dysfunction is observed with DM and insulin resistance. Our laboratory has reported failed vascular mitochondrial adaptation to exercise in DM rats. We hypothesize that repairing vascular mitochondrial function could restore contractility in DM. We employed primary aortic smooth muscle cells (SMC) from a lean, insulin resistant DM rat, Goto-Kakizaki (GK), and the Wistar (W) control to test mitochondrial adaptation to metabolic stress. SMC were exposed to low glucose (LG, 5 mM glucose) or high glucose (HG, 25mM) treatments for 1, 4 and 24 hours. Mitochondrial respiration, superoxide and dynamics (fission and fusion) were measured. Respiration in W SMC exposed to HG was unchanged compared to the LG control, but was decreased after 4 hours of HG treatment in the GK SMC (p≤0.05). GK SMC have significantly increased whole cell production of H 2 O 2 as compared to W SMC, but not mitochondrial superoxide after 4 hours of HG treatment. In contrast, W SMC exposed to HG significantly had increased superoxide relative to LG control (p<0.05). No differences in total mitochondrial complex expression were seen in baseline W and GK SMC comparisons; phosphorylated eNOS and PGC-1α, direct upstream regulators of mitochondrial biogenesis, were increased and decreased, respectively, in the GK SMC as compared to the W SMC (p<0.05). Preliminary quantitative immunohistochemistry shows a significant mitochondrial biogenesis and fusion response to the initial hour of HG treatment in the W SMC; conversely, GK SMC showed a decrease in mitochondria after 4 hours of HG treatment. Fis 1 was significantly decreased at 1 hour in W and increased at 24 hours in the GK (p<0.05). Significant changes in fusion included decreased OPA1 and mfn1 in W SMC and increased OPA1 and decreased mfn1 in the GK. Overall, these data reveal that distinct mitochondrial adaptation to a hyperglycemic state is persistent in DM cells ex vivo. Primary SMC can be used as a model to define signaling events determining these changes and development of therapeutic targets to repair contractility.

Abstract 165: Saxagliptin Restores Vascular Mitochondrial Exercise Response in Diabetes

Exercise decreases cardiovascular disease (CVD) risk and all-cause mortality. We and others have defined that exercise stimulates mitochondrial biogenesis via upstream signaling through endothelial nitric oxide synthase (eNOS), sirtuins (SIRTs), and/or PPARγ co-activator alpha (PGC1-α). Further, this response is absent in diabetes and hypertension. We tested the hypothesis that pharmacological restoration of vascular signaling with the dipeptidyl peptidase-4 (DPP-4) inhibitor saxagliptin will improve vascular mitochondrial adaptation to exercise through activation of eNOS, SIRTs, and/or PGC1-α. We examined the impact of an 8 day treadmill exercise intervention in the Goto-Kakizaki (GK) rat, a model of lean, type 2 diabetes (T2DM), and Wistar control rats. Four groups were examined: sedentary or exercise groups with or without saxagliptin. Twenty-four hours post-bout, aortas were probed for mitochondrial complexes I-V, as well upstream signaling molecules. In Wistar rats, the expression of mitochondrial complexes III, IV, and V, along with SIRT3 (p<0.05), eNOS, and PCG1-α, increased with exercise. Conversely, in GK animals, exercise led to a decrease of complexes I, III, and IV, a decrease in the expression of COX IV (p<0.05) and AMPK, and no effect on eNOS or SIRT3. In exercised GK rats treated with saxagliptin, the expression of all mitochondrial complexes increased, complex IV significantly (p<0.05). Significant increases (p<0.05) were also observed in cytochrome c, eNOS and nNOS, PGC1-α, and UCP3 protein content in GK rats treated with both exercise and saxagliptin. Body weight and insulin and glucose concentrations were not significantly different in GK animals across experimental groups, indicating that the effects observed are independent of changes in these parameters. In addition, saxagliptin added to a three week exercise intervention improved running time significantly compared to an exercise intervention alone. In summary, our data suggest that saxagliptin restores vascular mitochondrial adaptation to exercise in a rodent model of diabetes. In conclusion, these data are proof of concept of a targetable mitochondrial defect in the diabetic vasculature.

Are low-income elderly patients at risk for poor diabetes care?

OBJECTIVE

Diabetes is common among low-income elderly, dual-eligible (DE) Medicare/Medicaid patients resulting in significant morbidity, mortality, and cost. However, the quality of diabetes care delivered to these patients has not been evaluated. The aims of this study were to describe the quality of diabetes care provided to DE patients and compare it with non-DE patients.

RESEARCH DESIGN AND METHODS

This was a cross-sectional analysis of administrative claims from 1 January 1997 through 31 December 1998. A total of 9,453 patients aged 65-75 years with diabetes participated in the study. These were Colorado Medicare fee-for-service (FFS) outpatients. The main outcome measures consisted of a proportion of patients receiving an annual hemoglobin A1c test, biennial eye examination, biennial lipid test, and all three of these care processes.

RESULTS

The mean patient age was 71 +/- 2.8 years. Over 22% of patients were identified as dual eligible, and they were significantly more likely to be younger, female, and of minority race/ethnicity; reside in a rural location; and have comorbid conditions compared with the non-DE population. DE patients had more visits to primary care physicians, emergency departments, and hospitalizations but were less likely to visit endocrinologists. DE patients were significantly less likely to receive an annual A1c test (73 vs. 81%; P < 0.0001), biennial ophthalmologic examination (63 vs. 75%; P < 0.0001), and biennial lipid testing (43 vs. 57%; P < 0.0001). The adjusted odds ratio of urban DE patients receiving all three care measures was 0.60 (95% CI 0.52-0.69) compared with urban non-DE patients. Minority race/ethnicity and emergency department use were significantly associated with not receiving diabetes care, whereas endocrinology visits were associated with an increased odds of receiving diabetes care.

CONCLUSIONS

DE Medicare/Medicaid status was independently associated with not receiving diabetes care, especially among those in urban areas.

Odorant Stimulation Enhances Survival of Olfactory Sensory Neurons via MAPK and CREB

Olfactory sensory neurons (OSNs) can be sensitized to odorants by repeated exposure, suggesting that an animal's responsiveness to olfactory cues can be enhanced at the initial stage of detection. However, because OSNs undergo a regular cycle of apoptosis and replacement by ostensibly naive, precursor-derived neurons, the advantage of sensitization would be lost in the absence of a mechanism for odorant-enhanced survival of OSNs. Using recombinant adenoviruses in conjunction with surgical and electrophysiological techniques, we monitored OSN survival and function in vivo and find that odorant exposure selectively rescues populations of OSNs from apoptosis. We further demonstrate that odorant stimuli rescue OSNs in a cAMP-dependent manner by activating the MAPK/CREB-dependent transcriptional pathway, possibly as a result of expression of Bcl-2.

Diabetes-related changes in cAMP response element-binding protein content enhance smooth muscle cell proliferation and migration

We hypothesized that diabetes and glucose-induced reactive oxygen species lead to depletion of cAMP response element-binding protein (CREB) content in the vasculature. In primary cultures of smooth muscle cells (SMC) high medium glucose decreased CREB function but increased SMC chemokinesis and entry into the cell cycle. These effects were blocked by pretreatment with the antioxidants. High glucose increased intracellular reactive oxygen species detected by CM-H(2)DCFA. SMC exposed to oxidative stress (H(2)O(2)) demonstrated a 3.5-fold increase in chemokinesis (p < 0.05) and accelerated entry into cell cycle, accompanied by a significant decrease in CREB content. Chronic oxidative challenge similar to the microenvironment in diabetes (glucose oxidase treatment) decreases CREB content (40-50%). Adenoviral-mediated expression of constitutively active CREB abolished the increase in chemokinesis and cell cycle progression induced by either high glucose or oxidative stress. Analysis of vessels from insulin resistant or diabetic animals indicates that CREB content is decreased in the vascular stroma. Treatment of insulin-resistant animals with the insulin sensitizer rosiglitazone restores vessel wall CREB content toward that observed in normal animals. In summary, high glucose and oxidative stress decrease SMC CREB content increase chemokinesis and entry into the cell cycle, which is blocked by antioxidants or restoration of CREB content. Thus, decreased vascular CREB content could be one of the molecular mechanisms leading to increased atherosclerosis in diabetes.

cAMP response element-binding protein content is a molecular determinant of smooth muscle cell proliferation and migration

We hypothesized that cAMP response element-binding protein (CREB) could function as a molecular determinant of smooth muscle cell fate. In arterial sections from the systemic and pulmonary circulation, CREB content was high in proliferation-resistant medial subpopulations of smooth muscle cells and low in proliferation-prone regions. In vessels from neonatal calves exposed to chronic hypoxia, CREB content was depleted and smooth muscle cell (SMC) proliferation was accelerated. Induction of quiescence by serum deprivation in culture led to increased CREB content. Highly proliferative SMC in culture were observed to have low CREB content. Exposure to proliferative stimuli such as hypoxia or platelet-derived growth factor decreased SMC CREB content. Assessment of CREB gene transcription by nuclear run-on analysis and transcription from a CREB promoter-luciferase construct indicate that CREB levels in SMC are in part controlled at the level of transcription. Overexpression of wild type or constitutively active CREB in primary cultures of SMC arrested cell cycle progression. Additionally, expression of constitutively active CREB decreased both proliferation and chemokinesis. Consistent with these functional properties, active CREB decreased the expression of multiple cell cycle regulatory genes, as well as genes encoding growth factors, growth factor receptors, and cytokines. Our data suggest a unique mode of cellular phenotype determination at the level of the nuclear content of CREB.

Insulin-induced adipocyte differentiation. Activation of CREB rescues adipogenesis from the arrest caused by inhibition of prenylation

Insulin is a potent adipogenic hormone that triggers an induction of a series of transcription factors governing differentiation of pre-adipocytes into mature adipocytes. However, the exact link between the insulin signaling cascade and the intrinsic cascade of adipogenesis remains incompletely understood. Herein we demonstrate that inhibition of prenylation of p21ras and Rho-A arrests insulin-stimulated adipogenesis. Inhibition of farnesylation of p21ras also blocked the ability of insulin to activate mitogen-activated protein (MAP) kinase and cyclic AMP response element-binding (CREB) protein. Expression of two structurally different inducible constitutively active CREB constructs rescued insulin-stimulated adipocyte differentiation from the inhibitory influence of prenylation inhibitors. Constitutively active CREB constructs induced expression of PPARgamma2, fatty acid synthase, GLUT-4, and leptin both in control and prenylation inhibitors-treated cells. It appears that insulin-stimulated prenylation of the Ras family GTPases assures normal phosphorylation and activation of CREB that, in turn, triggers the intrinsic cascade of adipogenesis.

Akt/protein kinase B up-regulates Bcl-2 expression through cAMP-response element-binding protein

In our previous study we showed that insulin-like growth factor-I induces a cAMP-response element (CRE) site-containing Bcl-2 promoter through a novel signaling pathway involving mitogen-activated protein kinase kinase 6/p38beta mitogen-activated protein kinase/MAP kinase-activated protein kinase-3/cAMP-response element-binding protein (CREB) (Pugazhenthi, S., Miller, E., Sable, C., Young, P., Heidenreich, K. A., Boxer, L. M., and Reusch, J. E.-B. (1999) J. Biol. Chem. 274, 27529-27535). In the present investigation, we define a second pathway contributing to CREB-dependent up-regulation of Bcl-2 expression as a novel anti-apoptotic function of Akt signaling. To examine the role of Akt on Bcl-2 expression, a series of transient transfections using a luciferase reporter gene driven by the promoter region of Bcl-2 containing a CRE were carried out. Pharmacological inhibition of phosphatidylinositol (PI) 3-kinase, the upstream kinase of Akt, with LY294002 led to a 45% decrease in Bcl-2 promoter activity. The reporter activity was enhanced 2.3-fold by overexpression of active p110 subunit of PI 3-kinase and inhibited 44% by the dominant negative p85 subunit of PI 3-kinase. Cotransfection with 3-phosphoinositide-dependent kinase (PDK1), which is required for the full activation of Akt, resulted in enhanced luciferase activity. Insulin-like growth factor-I-mediated induction of Bcl-2 promoter activity was decreased significantly (p < 0.01) by the dominant negative forms of p85 subunit of PI 3-kinase, PDK1, and Akt. These data indicate that regulation of Bcl-2 expression by IGF-I involves a signaling cascade mediated by PI 3-kinase/PDK1/Akt/CREB. Furthermore, we measured the Bcl-2 mRNA in PC12 cells overexpressing Akt by real-time quantitative reverse transcription-polymerase chain reaction using the TaqMan(TM) fluorogenic probe system. We observed a 2.1-fold increase in Bcl-2 mRNA levels in the Akt cell line compared with control PC12 cells, supporting the observation that enhanced CREB activity by Akt signaling leads to increased Bcl-2 promoter activity and cell survival.

CREB activation induces adipogenesis in 3T3-L1 cells

Obesity is the result of numerous, interacting behavioral, physiological, and biochemical factors. One increasingly important factor is the generation of additional fat cells, or adipocytes, in response to excess feeding and/or large increases in body fat composition. The generation of new adipocytes is controlled by several "adipocyte-specific" transcription factors that regulate preadipocyte proliferation and adipogenesis. Generally these adipocyte-specific factors are expressed only following the induction of adipogenesis. The transcription factor(s) that are involved in initiating adipocyte differentiation have not been identified. Here we demonstrate that the transcription factor, CREB, is constitutively expressed in preadipocytes and throughout the differentiation process and that CREB is stimulated by conventional differentiation-inducing agents such as insulin, dexamethasone, and dibutyryl cAMP. Stably transfected 3T3-L1 preadipocytes were generated in which we could induce the expression of either a constitutively active CREB (VP16-CREB) or a dominant-negative CREB (KCREB). Inducible expression of VP16-CREB alone was sufficient to initiate adipogenesis as determined by triacylglycerol storage, cell morphology, and the expression of two adipocyte marker genes, peroxisome proliferator activated receptor gamma 2, and fatty acid binding protein. Alternatively, KCREB alone blocked adipogenesis in cells treated with conventional differentiation-inducing agents. These data indicate that activation of CREB was necessary and sufficient to induce adipogenesis. Finally, CREB was shown to bind to putative CRE sequences in the promoters of several adipocyte-specific genes. These data firmly establish CREB as a primary regulator of adipogenesis and suggest that CREB may play similar roles in other cells and tissues.

Effects of exercise training on oxygen uptake kinetic responses in women with type 2 diabetes

OBJECTIVE

Women with uncomplicated type 2 diabetes have both a decreased maximal oxygen consumption (VO2max) and slowed oxygen uptake (VO2) kinetics at the onset of exercise compared with nondiabetic women. These abnormalities are seen not only at maximal workloads, but also at the onset of low-level exercise. To evaluate the hypothesis that VO2max and VO2 kinetics would improve with exercise training in untrained people with type 2 diabetes, we measured these parameters in premenopausal sedentary women before and after 3 months of supervised exercise training.

RESEARCH DESIGN AND METHODS

A total of 8 women with type 2 diabetes, 9 overweight nondiabetic women, and 10 lean nondiabetic women were studied. At baseline and after 3 months of exercise training, subjects underwent bicycle ergometer testing to obtain VO2max and VO2 kinetics data.

RESULTS

On entry, women with type 2 diabetes had the lowest VO2max and slowest VO2 kinetics of the three groups. After exercise training, the women with type 2 diabetes improved their VO2max more than the lean and overweight control women: 28 vs. 5 and 8%, respectively (P < 0.05 for the diabetic group vs. both control groups). In the group with diabetes, VO2 kinetics improved by 39 and 22% at 20 and 30 W, respectively. For the control subjects, VO2 kinetics did not improve at any workload in either group.

CONCLUSIONS

Despite beginning with the lowest VO2max and slowest VO2 kinetics, subjects with type 2 diabetes benefited more from an exercise training program than did control subjects. These findings suggest that in addition to its known metabolic effects, exercise training in individuals with type 2 diabetes may be an effective therapy to improve the cardiovascular response to exercise and to overcome low-level exercise impairment as reflected by improved VO2max and VO2 kinetics. If the ability to make circulatory adjustments at the beginning of exercise at low workloads is improved by an exercise training program, as suggested by the VO2 kinetics data, the clinical significance of exercise for people with type 2 diabetes is clear.

Insulin-like growth factor-I induces bcl-2 promoter through the transcription factor cAMP-response element-binding protein

Insulin-like growth factor-I (IGF-I) is known to prevent apoptosis induced by diverse stimuli. The present study examined the effect of IGF-I on the promoter activity of bcl-2, a gene with antiapoptotic function. A luciferase reporter driven by the promoter region of bcl-2 from -1640 to -1287 base pairs upstream of the translation start site containing a cAMP-response element was used in transient transfection assays. Treatment of PC12 cells with IGF-I enhanced the bcl-2 promoter activity by 2.3-fold, which was inhibited significantly (p < 0.01) by SB203580, an inhibitor of p38 mitogen-activated protein kinase (MAPK). Cotransfection of the bcl-2 promoter with MAPK kinase 6 and the beta isozyme of p38 MAPK resulted in 2-3-fold increase in the reporter activity. The dominant negative form of MAPKAP-K3, a downstream kinase activated by p38 MAPK, and the dominant negative form of cAMP-response element-binding protein, inhibited the reporter gene activation by IGF-I and p38beta MAPK significantly (p < 0.01). IGF-I increased the activity of p38beta MAPK introduced into the cells by adenoviral infection. Thus, we have characterized a novel signaling pathway (MAPK kinase 6/p38beta MAPK/MAPKAP-K3) that defines a transcriptional mechanism for the induction of the antiapoptotic protein Bcl-2 by IGF-I through the nuclear transcription factor cAMP-response element-binding protein in PC12 cells.

Insulin-like growth factor I-mediated activation of the transcription factor cAMP response element-binding protein in PC12 cells. Involvement of p38 mitogen-activated protein kinase-mediated pathway

IGF-I is known to support growth and to prevent apoptosis in neuronal cells. Activation of the nuclear transcription factor cAMP response element-binding protein (CREB) has emerged as a central determinant in neuronal functions. In the present investigation, we examined the IGF-I-mediated phosphorylation and transcriptional activation of CREB in rat pheochromocytoma (PC12) cells, a cellular model for neuronal differentiation, and defined three distinct postreceptor signaling pathways important for this effect including the p38 mitogen-activated protein kinase (MAPK) pathway. CREB phosphorylation at serine 133 and its transcriptional activation as measured by a CREB-specific Gal4-CREB reporter and the neuroendocrine-specific gene chromogranin A was induced 2-3.3-fold by insulin-like growth factor (IGF)-I. This activation was significantly blocked (p < 0.001) by the dominant negative K-CREB or by mutation of the CRE site. IGF-I stimulated chromogranin A gene expression by Northern blot analysis 3.7-fold. Inhibition of MAPK kinase with PD98059, PI 3-kinase with wortmannin, and p38 MAPK with SB203580 blocked IGF-I-mediated phosphorylation and transcriptional activation of CREB by 30-50% (p < 0.001). Constitutively active and dominant negative regulators of the Ras and PI 3-kinase pathways confirmed the contribution of these pathways for CREB regulation by IGF-I. Cotransfection of PC12 cells with p38beta and constitutively active MAPK kinase 6 resulted in enhanced basal as well as IGF-I-stimulated chromogranin A promoter. IGF-I activated p38 MAPK, which was blocked by the inhibitor SB203580. This is the first description of a p38 MAPK-mediated nuclear signaling pathway for IGF-I leading to CREB-dependent neuronal specific gene expression.

Abnormal oxygen uptake kinetic responses in women with type II diabetes mellitus

Persons with type II diabetes mellitus (DM), even without cardiovascular complications have a decreased maximal oxygen consumption (VO2 max) and submaximal oxygen consumption (VO2) during graded exercise compared with healthy controls. We evaluated the hypothesis that change in the rate of VO2 in response to the onset of constant-load exercise (measured by VO2-uptake kinetics) was slowed in persons with type II DM. Ten premenopausal women with uncomplicated type II DM, 10 overweight, nondiabetic women, and 10 lean, nondiabetic women had a VO2 max test. On two separate occasions, subjects performed 7-min bouts of constant-load bicycle exercise at workloads below and above the lactate threshold to enable measurements of VO2 kinetics and heart rate kinetics (measuring rate of heart rate rise). VO2 max was reduced in subjects with type II DM compared with both lean and overweight controls (P < 0.05). Subjects with type II DM had slower VO2 and heart rate kinetics than did controls at constant workloads below the lactate threshold. The data suggest a notable abnormality in the cardiopulmonary response at the onset of exercise in people with type II DM. The findings may reflect impaired cardiac responses to exercise, although an additional defect in skeletal muscle oxygen diffusion or mitochondrial oxygen utilization is also possible.

Focus on insulin resistance in type 2 diabetes: therapeutic implications

Type 2 diabetes is extremely common and increasing in the United States. The pathophysiology of type 2 diabetes is a combination of increased insulin resistance and inadequate secretion. The main risk factors for diabetes are family history, obesity, sedentary lifestyle, ethnic background, age, and a history of gestational diabetes. Diet and exercise, the cornerstones of diabetes management, will improve insulin sensitivity and indirectly augment insulin secretion. Until recently, the only pharmacological approaches to diabetes were sulfonylureas and insulin, which either augment insulin secretion or replace insulin, thus acting only on the insulin side of the equation. Recently, a series of new drugs have become available that are capable of decreasing hepatic glucose output (metformin), slowing postprandial glucose absorption (acarbose), and improving peripheral insulin sensitivity (troglitazone). With these drugs, either alone or in combination, and behavioral therapies, it is now feasible to achieve good to outstanding glycemic control in most individuals with type 2 diabetes.

Insulin stimulates cAMP-response element binding protein activity in HepG2 and 3T3-L1 cell lines

Earlier studies from our laboratory demonstrated an insulin-mediated increase in cAMP-response element binding protein (CREB) phosphorylation. In this report, we show that insulin stimulates both CREB phosphorylation and transcriptional activation in HepG2 and 3T3-L1 cell lines, models of insulin-sensitive tissues. Insulin stimulated the phosphorylation of CREB at serine 133, the protein kinase A site, and mutation of serine 133 to alanine blocked the insulin effect. Many of the signaling pathways known to be activated by insulin have been implicated in CREB phosphorylation and activation. The ability of insulin to induce CREB phosphorylation and activity was efficiently blocked by PD98059, a potent inhibitor of mitogen-activated protein kinase kinase (MEK1), but not significantly by rapamycin or wortmannin. Likewise, expression of dominant negative forms of Ras or Raf-1 completely blocked insulin-stimulated CREB transcriptional activity. Finally, we demonstrate an essential role for CREB in insulin activation of fatty-acid synthase and fatty acid binding protein (FABP) indicating the potential physiologic relevance of insulin regulation of CREB. In summary, insulin regulates CREB transcriptional activity in insulin-sensitive tissues via the Raf --> MEK pathway and has an impact on physiologically relevant genes in these cells.

Reduced phosphorylation of mitogen-activated protein kinase kinase in response to insulin in cells with truncated C-terminal domain of insulin receptor

Insulin-stimulated activity of Raf-1 kinase was examined in Rat-1 fibroblasts transfected with wild-type and mutant human insulin receptors. Insulin stimulated Raf-1 binding to p21Ras in HIRc (wild-type), delta CT (insulin receptor lacking a 43-amino acid C-terminal domain), and Y/F2 (tyrosine 1316 and 1322 replaced by phenylalanine) cells. Despite equal binding to p21Ras, the activity of Raf-1 kinase (measured by phosphorylation of its downstream substrate, mitogen-activated protein/extracellular receptor kinase (MEK) was significantly reduced in the delta CT cells. As an association of Raf-1 with p21Ras does not activate Raf-1 kinase, but merely targets Raf-1 to the plasma membrane, we examined the binding of Raf-1 to 14-3-3 proteins and to the insulin receptor itself. Raf-1 was detected in both 14-3-3 and insulin receptor immunoprecipitates. Association of Raf-1 with either 14-3-3 protein or insulin receptor was not influenced by insulin and was similar in all control and insulin-treated cell lines. These results indicate that the delta CT cells are deficient in stimulating Raf-1 activity despite normal binding of Raf-1 to p21Ras. Thus, an unidentified mechanism of Raf-1 activation at the plasma membrane must be impaired in these cells.

Functional interactions of phosphatidylinositol 3-kinase with GTPase-activating protein in 3T3-L1 adipocytes

The role of phosphatidylinositol (PI) 3-kinase in specific aspects of insulin signaling was explored in 3T3-L1 adipocytes. Inhibition of PI 3-kinase activity by LY294002 or wortmannin significantly enhanced basal and insulin-stimulated GTPase-activating protein (GAP) activity in 3T3-L1 adipocytes. Furthermore, removal of the inhibitory influence of PI 3-kinase on GAP resulted in dose-dependent decreases in the ability of insulin to stimulate p21ras. This effect was specific to adipocytes, as inhibition of PI 3-kinase did not influence GAP in either 3T3-L1 fibroblasts, Rat-1 fibroblasts, or CHO cells. Immunodepletion of either of the two subunits of the PI 3-kinase (p85 or p110) yielded similar activation of GAP, suggesting that catalytic activity of p110 plays an important role in controlling GAP activity in 3T3-L1 adipocytes. Inhibition of PI 3-kinase activity in 3T3-L1 adipocytes resulted in abrogation of insulin-stimulated glucose uptake and thymidine incorporation. In contrast, effects of insulin on glycogen synthase and mitogen-activated protein kinase activity were inhibited only at higher concentrations of LY294002. It appears that in adipocytes, P1 3-kinase prevents activation of GAP. Inhibition of PI 3-kinase activity or immunodepletion of either one of its subunits results in activation of GAP and decreases in GTP loading of p21ras.

Insulin inhibits nuclear phosphatase activity: requirement for the C-terminal domain of the insulin receptor

Insulin's interaction with its receptor initiates a multitude of cellular effects on metabolism, growth, and differentiation. We recently described an insulin-mediated inhibition of nuclear protein phosphatase 2A (PP-2A), which is associated with an increase in phosphorylation of the transcription factor cAMP response element-binding protein. To clarify the role of nuclear PP-2A inhibition in the insulin signaling cascade, we examined the regulation of this phosphatase activity by insulin in Rat-1 fibroblasts overexpressing normal (HIRc) or mutant human insulin receptors (delta CT cells, deletion of a 43-amino acid C-terminal domain). The delta CT cells represent an excellent model of impaired metabolic and intact mitogenic action of insulin. Insulin inhibited nuclear PP-2A activity and enhanced cAMP response element-binding protein phosphorylation in HIRc cells, but not in delta CT cells. The delta CT cells exhibited normal ras activation and blunted mitogen-activating protein kinase phosphorylation and activation in response to insulin (16-fold in HIRc cells vs. 3-fold in delta CT cells), indicating that the mitogen-activating protein kinase pathway is important for the regulation of nuclear PP-2A activity by insulin. We conclude that insulin inhibits nuclear PP-2A activity, and that the carboxy-terminal domain of the insulin receptor is important for this effect.

Differential requirement for p21ras activation in the metabolic signaling by insulin

To evaluate the role of the "Ras pathway" in mediating metabolic signaling by insulin, we employed lovastatin to exhibit isoprenilation of Ras proteins in Rat-1 fibroblasts transfected with human insulin receptors (HIRc cells) and in differentiated 3T3-L1 adipocytes. Lovastatin blocked an ability of insulin to activate p21ras and mitogen-activated protein kinase. Lovastatin also significantly (p < 0.01) reduced insulin effects on thymidine incorporation and glucose incorporation into glycogen. Nevertheless, an effect of insulin on glucose uptake remained unaffected. It appears that in contrast to its mitogenic action and to its effect on glycogenesis, an effect of insulin on glucose uptake does not require p21ras activation.

Insulin inhibits dephosphorylation of adenosine 3',5'-monophosphate response element-binding protein/activating transcription factor-1: effect on nuclear phosphoserine phosphatase-2a

We examined the effects of insulin on the phosphorylation state of cAMP response element-binding protein (CREB) in normal rat adipocytes. Insulin increased in vivo phosphorylation of CREB by 40%. Although both phosphoprotein phosphatase-1 and -2A dephosphorylate CREB and activating transcription factor-1, insulin action appears to be mediated via its strong inhibitory effect on nuclear phosphatase-2A (PP-2A) activity. Using in vitro protein kinase-A-phosphorylated activating transcription factor-1 as a substrate, we found that insulin inhibited nuclear PP-2A activity by 80% (P < 0.001), which represents approximately 50% of the total nuclear phosphatase activity. Greater than 50% of the effect of insulin was observed at 0.3 nM and 2 min of exposure. These findings are the first indicator that a signal initiated by a cell surface tyrosine kinase receptor may regulate nuclear PP-2A activity and thereby affect the phosphorylation state of transcription factors.

GLUT-4 phosphorylation and its intrinsic activity. Mechanism of Ca(2+)-induced inhibition of insulin-stimulated glucose transport

In this study, we examined the influence of high levels of cytosolic calcium on phosphorylation status and function of GLUT-4 in isolated rat adipocytes. Intracellular calcium was elevated by exposing adipocytes to either extracellular ATP (1.6 mM) or thapsigargin (100 nM). Both agents increased cytosolic calcium 2-3 fold. While basal glucose uptake was unaffected, both ATP and thapsigargin reduced insulin-stimulated glucose transport by 40-70% (p < 0.05). Neither ATP nor thapsigargin affected GLUT-4 content or its translocation from the low density microsomes to the plasma membrane (PM). In contrast, GLUT-4 immunoprecipitated from the PM of adipocytes exposed to either ATP or thapsigargin was phosphorylated to a greater extent than the GLUT-4 isolated from control cells. ATP and thapsigargin also abolished insulin-stimulated dephosphorylation of GLUT-4. At the same time, GLUT-4 intrinsic activity was significantly reduced in adipocytes with high levels of cytosolic calcium (p < 0.05). Preincubation of adipocytes with cAMP antagonist, RpcAMP (10(-4) M), and calcium channel blocker, nitrendipine (30 microM), improved the ability of insulin to dephosphorylate GLUT-4 and restored insulin-stimulated GLUT-4 intrinsic activity. We conclude that elevated levels of cytosolic calcium interfere with insulin's ability to dephosphorylate GLUT-4, thus reducing its intrinsic activity.

Inverse relationship between GLUT-4 phosphorylation and its intrinsic activity

In this study, we examined the effect of phosphorylation on GLUT-4 function in isolated rat adipocytes. Adipocytes labeled with 32P for 2 h were incubated with parathyroid hormone (PTH) (20 ng/ml) for 60 min and then exposed to insulin (25 ng/ml) for an additional 30 min. 32P-GLUT-4 was immunoprecipitated from the plasma membrane and low density microsomal fractions, and its degree of phosphorylation was determined by autoradiography and densitometry. Results were expressed as 32P-GLUT-4 specific activity (phosphorylation/unit of protein). GLUT-4 intrinsic activity was measured using [14C]2-deoxyglucose uptake in plasma membrane vesicles. PTH significantly increased GLUT-4 phosphorylation and eliminated the insulin-stimulated dephosphorylation of GLUT-4. Western blotting revealed normal distribution of GLUT-4 before and after insulin stimulation in control and PTH-treated cells, suggesting that phosphorylation of GLUT-4 does not interfere with its recruitment to the plasma membrane. In contrast, intrinsic activity of phosphorylated GLUT-4 was significantly reduced (p < 0.01). Preincubation of adipocytes with calcium channel blocker (nitrendipine) and cyclic AMP antagonist (RpcAMP) restored GLUT-4 intrinsic activity in the PTH-treated cells. In several experiments, GLUT-4 was phosphorylated in vitro in plasma membrane vesicles isolated from normal adipocytes exposed to insulin. This in vitro phosphorylation reduced GLUT-4 intrinsic activity by approximately 35% (p < 0.01). We conclude that phosphorylation of GLUT-4 significantly impairs the ability of insulin to stimulate its intrinsic activity.

Preoperative diagnosis of lymphocytic hypophysitis (adenohypophysitis) unresponsive to short course dexamethasone: case report

Lymphocytic hypophysitis (adenohypophysitis) is a rare lymphocytic infiltration of the pituitary gland that usually occurs during pregnancy. Because of its rarity, it has seldom been diagnosed preoperatively, and no trials of therapeutic treatment have been reported to date. We describe a 29-year-old woman with a pituitary mass and visual-field defects during pregnancy. The patient's pituitary profile revealed an abnormal thyroid axis and relatively low prolactin for her stage of pregnancy. This finding suggested adenohypophysitis, and the patient was given a trial course of dexamethasone. The progression of the visual-field defects, however, indicated that the steroids, both in dosage and duration, were not effective. Thus, the patient underwent a partial hypophysectomy for decompression. The pathology report confirmed adenohypophysitis, and steroids were continued for the remainder of the pregnancy, with slow resolution of the visual-field defects to normal. This report is the first case of adenohypophysitis where the diagnosis was suspected preoperatively, and a trial course of steroids was given. The steroids at the dosage and duration used were not effective. Further evaluation of the use of steroids in this disease is warranted.

Regulation of GLUT-4 phosphorylation by intracellular calcium in adipocytes

Sustained elevations in cytosolic calcium concentrations ([Ca2+]i) have been shown to render insulin target cells resistant to insulin action. In this study we examined the mechanisms of the detrimental effect of high levels of [Ca2+]i on insulin-induced 2-deoxyglucose (2-DOG) uptake. To elevate [Ca2+]i, we incubated rat adipocytes with either 40 mM potassium (K+) or 20 ng/ml PTH for 1 h for in vitro experiments and injected rats with PTH (injections of 50 micrograms, ip, every hour for 3 h) for in vivo studies. Adipocytes with elevated [Ca2+]i demonstrated a 30% decrease in insulin-stimulated 2-DOG uptake. A calcium channel blocker (nitrendipine) and a cAMP antagonist (RpcAMP) each partially restored insulin-stimulated glucose transport, but together they completely restored 2-DOG uptake. Concomitantly, we found a significant increase in phosphorylation of GLUT-4 in adipocytes with elevated [Ca2+]i. This change in GLUT-4 phosphorylation was also attenuated by nitrendipine and RpcAMP. These observations confirm that elevated [Ca2+]i diminishes insulin-stimulated glucose transport and suggest that increased phosphorylation of GLUT-4 in adipocytes with high [Ca2+]i may alter its intrinsic activity.

Cisplatin chronotherapy and disulfiram rescue reduce toxicity without interfering with anticancer activity: animal findings and preliminary clinical experiences

Cisplatin-induced mortality and nephrotoxicity are each predictably worse when the drug is given at certain points within the circadian schedule. Oral disulfiram protects rats from toxic effects at some circadian stages but not others. This manuever does not diminish the anticancer activity of cisplatin in these rats. Human beings given 2 g of oral disulfiram and high doses of cisplatin at the circadian stage associated with least cisplatin nephrotoxicity (prospectively determined potassium excretion acrophase) suffer little or no kidney damage. Disulfiram administration apparently does not interfere with the antineoplastic activity of cisplatin in humans. This is the first demonstration of the feasibility of assignment of treatment time according to a measure of the patient's 'internal clock' as assessed by pretreatment marker rhythmometry. It also establishes the feasibility of giving disulfiram to human beings.