Left ventricular dysfunction with reduced functional cardiac reserve in diabetic and non-diabetic LDL-receptor deficient apolipoprotein B100-only mice

Assessing systolic and diastolic reserves in male and female mice

Cardiac reserve is a widely used health indicator and prognostic tool. Although it is well established how to assess cardiac reserve clinically, in preclinical models, it is more challenging lacking standardization. Furthermore, although cardiac reserve incorporates both systolic (i.e., contractile reserve) and diastolic (i.e., relaxation reserve) components of the cardiac cycle, less focus has been placed on diastolic reserve. The aim of our study was to determine which technique (i.e., echocardiography, invasive hemodynamic, and Langendorff) and corresponding parameters can be used to assess the systolic and diastolic reserves in preclinical models. Healthy adult male and female CD-1 mice were administered dobutamine and evaluated by echocardiography and invasive hemodynamic, or Langendorff to establish systolic and diastolic reserves. Here, we show that systolic reserve can be assessed using all techniques in vivo and in vitro. Yet, the current indices available are ineffective at capturing diastolic reserve of healthy mice in vivo. When assessing systolic reserve, sex affects the dose response of several commonly used echocardiography parameters [i.e., fractional shortening (FS), ejection fraction (EF)]. Taken together, this study improves our understanding of how sex impacts the interpretation assessment of cardiac reserve and establishes for the first time that in healthy adult mice, the diastolic reserve cannot be assessed by currently established methods in vivo.NEW & NOTEWORTHY Cardiac reserve is a globally used health indicator and prognostic tool that is used by clinicians and preclinical scientists. In physiology, we have a long-standing appreciation of how to assess systolic reserve but lack insight into sex differences and have no frame of reference for measuring diastolic reserve to certainty across cardiac techniques or the influence of sex. Here, we show that the primary means for assessing diastolic reserve is incorrect. Furthermore, we provided proof and clarity on how to correctly measure systolic and diastolic reserve capacities. We also highlight the imperative of sex differences to the measures of both systolic and diastolic reserves using several techniques (i.e., echocardiography, invasive hemodynamics, and Langendorff) in mice.

In vivo inhibition of nuclear factor of activated T-cells leads to atherosclerotic plaque regression in IGF-II/LDLR-/-ApoB100/100 mice

AIMS

Despite vast clinical experience linking diabetes and atherosclerosis, the molecular mechanisms leading to accelerated vascular damage are still unclear. Here, we investigated the effects of nuclear factor of activated T-cells inhibition on plaque burden in a novel mouse model of type 2 diabetes that better replicates human disease.

METHODS & RESULTS

IGF-II/LDLR-/-ApoB100/100 mice were generated by crossbreeding low-density lipoprotein receptor-deficient mice that synthesize only apolipoprotein B100 (LDLR-/-ApoB100/100) with transgenic mice overexpressing insulin-like growth factor-II in pancreatic β cells. Mice have mild hyperglycaemia and hyperinsulinaemia and develop complex atherosclerotic lesions. In vivo treatment with the nuclear factor of activated T-cells blocker A-285222 for 4 weeks reduced atherosclerotic plaque area and degree of stenosis in the brachiocephalic artery of IGF-II/LDLR-/-ApoB100/100 mice, as assessed non-invasively using ultrasound biomicroscopy prior and after treatment, and histologically after termination. Treatment had no impact on plaque composition (i.e. muscle, collagen, macrophages). The reduced plaque area could not be explained by effects of A-285222 on plasma glucose, insulin or lipids. Inhibition of nuclear factor of activated T-cells was associated with increased expression of atheroprotective NOX4 and of the anti-oxidant enzyme catalase in aortic vascular smooth muscle cells.

CONCLUSION

Targeting the nuclear factor of activated T-cells signalling pathway may be an attractive approach for the treatment of diabetic macrovascular complications.

Increased Calcific Aortic Valve Disease in response to a diabetogenic, procalcific diet in the LDLr-/-ApoB100/100 mouse model

OBJECTIVE

Calcific aortic valve disease (CAVD) is a major cause of aortic stenosis (AS) and cardiac insufficiency. Patients with type II diabetes mellitus (T2DM) are at heightened risk for CAVD, and their valves have greater calcification than nondiabetic valves. No drugs to prevent or treat CAVD exist, and animal models that might help identify therapeutic targets are sorely lacking. To develop an animal model mimicking the structural and functional features of CAVD in people with T2DM, we tested a diabetogenic, procalcific diet and its effect on the incidence and severity of CAVD and AS in the, LDLr-/-ApoB100/100 mouse model.

RESULTS

LDLr-/-ApoB100/100 mice fed a customized diabetogenic, procalcific diet (DB diet) developed hyperglycemia, hyperlipidemia, increased atherosclerosis, and obesity when compared with normal chow fed LDLr-/-ApoB100/100 mice, indicating the development of T2DM and metabolic syndrome. Transthoracic echocardiography revealed that LDLr-/-ApoB100/100 mice fed the DB diet had 77% incidence of hemodynamically significant AS, and developed thickened aortic valve leaflets and calcification in both valve leaflets and hinge regions. In comparison, normal chow (NC) fed LDLr-/-ApoB100/100 mice had 38% incidence of AS, thinner valve leaflets and very little valve and hinge calcification. Further, the DB diet fed mice with AS showed significantly impaired cardiac function as determined by reduced ejection fraction and fractional shortening. In vitro mineralization experiments demonstrated that elevated glucose in culture medium enhanced valve interstitial cell (VIC) matrix calcium deposition.

CONCLUSIONS

By manipulating the diet we developed a new model of CAVD in T2DM, hyperlipidemic LDLr-/-ApoB100/100 that shows several important functional, and structural features similar to CAVD found in people with T2DM and atherosclerosis including AS, cardiac dysfunction, and inflamed and calcified thickened valve cusps. Importantly, the high AS incidence of this diabetic model may be useful for mechanistic and translational studies aimed at development of novel treatments for CAVD.

Arterial Calcification in Diabetes Mellitus: Preclinical Models and Translational Implications

Diabetes mellitus increasingly afflicts our aging and dysmetabolic population. Type 2 diabetes mellitus and the antecedent metabolic syndrome represent the vast majority of the disease burden-increasingly prevalent in children and older adults. However, type 1 diabetes mellitus is also advancing in preadolescent children. As such, a crushing wave of cardiometabolic disease burden now faces our society. Arteriosclerotic calcification is increased in metabolic syndrome, type 2 diabetes mellitus, and type 1 diabetes mellitus-impairing conduit vessel compliance and function, thereby increasing the risk for dementia, stroke, heart attack, limb ischemia, renal insufficiency, and lower extremity amputation. Preclinical models of these dysmetabolic settings have provided insights into the pathobiology of arterial calcification. Osteochondrogenic morphogens in the BMP-Wnt signaling relay and transcriptional regulatory programs driven by Msx and Runx gene families are entrained to innate immune responses-responses activated by the dysmetabolic state-to direct arterial matrix deposition and mineralization. Recent studies implicate the endothelial-mesenchymal transition in contributing to the phenotypic drift of mineralizing vascular progenitors. In this brief overview, we discuss preclinical disease models that provide mechanistic insights-and point to challenges and opportunities to translate these insights into new therapeutic strategies for our patients afflicted with diabetes mellitus and its arteriosclerotic complications.

LRP5/canonical Wnt signalling and healing of ischemic myocardium

LRP5 (low-density lipoprotein receptor-related protein 5) activates canonical Wnt signalling. LRP5 plays multiple roles including regulation of lipoprotein and cholesterol homeostasis as well as innate immunity cell function. However, it is not known whether LRP5 has a role in the myocardium. The aim of this study was to investigate LRP5 and Wnt signalling in myocardial remodelling after acute myocardial infarction (MI). Wnt protein levels were determined in a hypercholesterolemic porcine model of MI, in Lrp5 ^-/- C57Bl6 mice, in cultured cardiomyocytes and in human explanted hearts with previous MI episodes. 21 days post-MI, there was upregulation of LRP5 in the ischemic myocardium of hypercholesterolemic pigs as well as an upregulated expression of proteins of the Wnt pathway. We demonstrate via overexpression and silencing experiments that LRP5 induces Wnt pathway activation in isolated cardiomyocytes. Hypoxia and lipid-loading induced the expression of Wnt proteins, whereas this effect is blocked in LRP5-silenced cardiomyocytes. To characterize the function of the LRP5-Wnt axis upregulation in the heart, we induced MI in wild-type and Lrp5 ^-/- mice. Lrp5 ^-/- mice had significantly larger infarcts than Wt mice, indicating a protective role of LRP5 in injured myocardium. The LRP5 upregulation in post-MI hearts seen in pigs and mice was also evident in human hearts as dyslipidemic patients with previous episodes of ischemia have higher expression of LRP5 and Wnt-signalling genes than non-ischemic dilated hearts. We demonstrate an upregulation of LRP5 and the Wnt signalling pathway that it is a prosurvival healing response of cardiomyocytes upon injury.

Ivabradine and metoprolol differentially affect cardiac glucose metabolism despite similar heart rate reduction in a mouse model of dyslipidemia

While heart rate reduction (HRR) is a target for the management of patients with heart disease, contradictory results were reported using ivabradine, which selectively inhibits the pacemaker I_f current, vs. β-blockers like metoprolol. This study aimed at testing whether similar HRR with ivabradine vs. metoprolol differentially modulates cardiac energy substrate metabolism, a factor determinant for cardiac function, in a mouse model of dyslipidemia (hApoB^+/+;LDLR^-/-). Following a longitudinal study design, we used 3- and 6-mo-old mice, untreated or treated for 3 mo with ivabradine or metoprolol. Cardiac function was evaluated in vivo and ex vivo in working hearts perfused with ¹³C-labeled substrates to assess substrate fluxes through energy metabolic pathways. Compared with 3-mo-old, 6-mo-old dyslipidemic mice had similar cardiac hemodynamics in vivo but impaired (P < 0.001) contractile function (aortic flow: -45%; cardiac output: -34%; stroke volume: -35%) and glycolysis (-24%) ex vivo. Despite inducing a similar 10% HRR, ivabradine-treated hearts displayed significantly higher stroke volume values and glycolysis vs. their metoprolol-treated counterparts ex vivo, values for the ivabradine group being often not significantly different from 3-mo-old mice. Further analyses highlighted additional significant cardiac alterations with disease progression, namely in the total tissue level of proteins modified by O-linked N-acetylglucosamine (O-GlcNAc), whose formation is governed by glucose metabolism via the hexosamine biosynthetic pathway, which showed a similar pattern with ivabradine vs. metoprolol treatment. Collectively, our results emphasize the implication of alterations in cardiac glucose metabolism and signaling linked to disease progression in our mouse model. Despite similar HRR, ivabradine, but not metoprolol, preserved cardiac function and glucose metabolism during disease progression.

Drug Target Identification and Validation: Global Pharmaceutical Industry Experts on Challenges, Best Strategies, Innovative Precompetitive Collaboration Concepts, and Future Areas of Industry Precompetitive Research and Development

Focused interviews were conducted with global pharmaceutical company representatives in order to derive a consistent view on drug target identification/validation challenges, collaborative strategies, and future developments in a precompetitive space. Analysis revealed translation into clinical utility as a major hurdle of novel drug target validation, originating from lack of biological understanding, irreproducibility of published results, and lack of valid animal models. Direct and close collaborations with academia are the preferred model to tackle basic research on novel drug targets in high-risk projects. Efforts to conduct target identification in large precompetitive consortia are acknowledged with some doubts about the pace of progress and data-sharing policies, while concept to extend the precompetitive space to target validation in phase II trials was curtailed to niche indications together with a revision of current intellectual property (IP) practice. Public-private partnerships in established areas are forecasted to increase. Novel emerging themes are toxicology data sharing, joint genetic patient data analysis, and reimbursement concepts.

Type 2 diabetes enhances arterial uptake of choline in atherosclerotic mice: an imaging study with positron emission tomography tracer ¹⁸F-fluoromethylcholine

Background

Diabetes is a risk factor for atherosclerosis associated with oxidative stress, inflammation and cell proliferation. The purpose of this study was to evaluate arterial choline uptake and its relationship to atherosclerotic inflammation in diabetic and non-diabetic hypercholesterolemic mice.

Methods

Low-density lipoprotein-receptor deficient mice expressing only apolipoprotein B100, with or without type 2 diabetes caused by pancreatic overexpression of insulin-like growth factor II (IGF-II/LDLR^−/−ApoB^100/100 and LDLR^−/−ApoB^100/100) were studied. Distribution kinetics of choline analogue ¹⁸F-fluoromethylcholine (¹⁸F-FMCH) was assessed in vivo by positron emission tomography (PET) imaging. Then, aortic uptakes of ¹⁸F-FMCH and glucose analogue ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG), were assessed ex vivo by gamma counting and autoradiography of tissue sections. The ¹⁸F-FMCH uptake in atherosclerotic plaques was further compared with macrophage infiltration and the plasma levels of cytokines and metabolic markers.

Results

The aortas of all hypercholesterolemic mice showed large, macrophage-rich atherosclerotic plaques. The plaque burden and densities of macrophage subtypes were similar in diabetic and non-diabetic animals. The blood clearance of ¹⁸F-FMCH was rapid. Both the absolute ¹⁸F-FMCH uptake in the aorta and the aorta-to-blood uptake ratio were higher in diabetic than in non-diabetic mice. In autoradiography, the highest ¹⁸F-FMCH uptake co-localized with macrophage-rich atherosclerotic plaques. ¹⁸F-FMCH uptake in plaques correlated with levels of total cholesterol, insulin, C-peptide and leptin. In comparison with ¹⁸F-FDG, ¹⁸F-FMCH provided similar or higher plaque-to-background ratios in diabetic mice.

Conclusions

Type 2 diabetes enhances the uptake of choline that reflects inflammation in atherosclerotic plaques in mice. PET tracer ¹⁸F-FMCH is a potential tool to study vascular inflammation associated with diabetes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-016-0340-6) contains supplementary material, which is available to authorized users.

Animal models of diabetic macrovascular complications: key players in the development of new therapeutic approaches

Diabetes mellitus is a lifelong, incapacitating metabolic disease associated with chronic macrovascular complications (coronary heart disease, stroke, and peripheral vascular disease) and microvascular disorders leading to damage of the kidneys (nephropathy) and eyes (retinopathy). Based on the current trends, the rising prevalence of diabetes worldwide will lead to increased cardiovascular morbidity and mortality. Therefore, novel means to prevent and treat these complications are needed. Under the auspices of the IMI (Innovative Medicines Initiative), the SUMMIT (SUrrogate markers for Micro- and Macrovascular hard end points for Innovative diabetes Tools) consortium is working on the development of novel animal models that better replicate vascular complications of diabetes and on the characterization of the available models. In the past years, with the high level of genomic information available and more advanced molecular tools, a very large number of models has been created. Selecting the right model for a specific study is not a trivial task and will have an impact on the study results and their interpretation. This review gathers information on the available experimental animal models of diabetic macrovascular complications and evaluates their pros and cons for research purposes as well as for drug development.

[18F]fluorodeoxyglucose uptake in atherosclerotic plaques is associated with reduced coronary flow reserve in mice

OBJECTIVES

Coronary microvascular dysfunction, observed as impaired coronary vasodilator capacity, is an early manifestation of coronary artery disease. Inflammation plays an important role in different stages of atherogenesis. To study the role of vessel wall inflammation in the development of coronary dysfunction, we compared [(18)F]fluorodeoxyglucose (FDG) uptake in the aorta and coronary flow reserve (CFR) in atherosclerotic mice.

METHODS

We studied healthy young C57BL/6 mice fed a normal diet (n = 7) as well as hypercholesterolemic low-density lipoprotein receptor-disrupted/apolipoprotein B100-expressing (LDLR(-/-)ApoB(100/100)) mice (n = 15) and hypercholesterolemic and diabetic LDLR(-/-)ApoB(100/100)insulinlike growth factor II-overexpressing mice (n = 14) fed a western-type diet, aged 4 to 6 months. Doppler sonography was used to measure CFR as the ratio of coronary flow velocity during isoflurane-induced hyperemia and at rest. Uptake of [(18)F]FDG into the aorta was measured by autoradiography of tissue sections.

RESULTS

Histologic sections showed extensive atherosclerosis in the aorta, but coronary arteries were not obstructed. Both hyperemic coronary flow velocity and CFR were reduced (P < .05) in hypercholesterolemic mice with and without diabetes in comparison to healthy young C57BL/6 controls. Among hypercholesterolemic mice, both hyperemic flow velocity and CFR inversely correlated with atherosclerotic plaque [(18)F]FDG uptake in the aorta (r = -0.73; P < .001; r = -0.63; P = .001, respectively). In a multivariate analysis, including animal weight, aortic plaque burden, plasma glucose, plasma cholesterol, and [(18)F]FDG uptake in atherosclerotic plaques, only [(18)F]FDG uptake remained an independent predictor of reduced CFR (β = 0.736; P = .001).

CONCLUSIONS

The inflammatory activity in atherosclerotic plaques of the aorta independently predicts reduced CFR in atherosclerotic mice without obstructive coronary artery disease. This finding suggests that atherosclerotic inflammation contributes to coronary dysfunction.

Glibenclamide attenuates myocardial injury by lipopolysaccharides in streptozotocin-induced diabetic mice

BACKGROUND

Sepsis is a common disease that continues to increase in incidence in the world. Diseases, such as diabetes mellitus, may make the situation worse. Diabetic patients are at increased risk for common infections. This study was designed to investigate the role of glibenclamide on myocardial injury by lipopolysaccharides (LPS) in streptozotocin induced diabetic mice (STZ-mice).

METHODS

LPS was used to induce endotoxemia in STZ-mice. Heart rate and mean arterial pressure were measured by MPA-HBBS. Serum epinephrine level was measured by enzyme-linked immunosorbent assays (ELISA). Myocardial injury was examined by light and transmission electron microscope and TUNEL staining. Macrophage infiltration was measured by immunohistochemistry. Interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) levels in myocardial tissue and serum in STZ-mice, and in conditional medium of primary cultured peritoneal macrophages were determined by ELISA. Nalp3 and Caspase-1 protein levels were measured by Western blotting analysis.

RESULTS

STZ administration decreased body weight and increased blood glucose in C57BL/6 mice. LPS injection caused decreases of heart rate and mean arterial pressure, and elevated serum epinephrine level in C57BL/6 mice. Compared with control mice without STZ treatment, LPS induced more severe myocardial injury and macrophage infiltration in STZ-mice, which was attenuated by pretreatment of glibenclamide. LPS stimulation enhanced the levels of IL-1β and TNF-α in both cardiac tissue and serum. Glibenclamide pretreatment significantly inhibited the serum levels of pro-inflammatory cytokines. Either high glucose or LPS increased the levels of IL-1β and TNF-α in the conditional medium of peritoneal macrophages. Glibenclamide treatment suppressed the increase of IL-1β level induced by high glucose and LPS. Furthermore, Nalp3 and Caspase-1 levels were markedly increased by high glucose plus LPS, and both proteins were significantly inhibited by glibenclamide treatment.

CONCLUSIONS

We conclude that glibenclamide could attenuate myocardial injury induced by LPS challenge in STZ-mice, which was possibly related to inhibiting inflammation through Nalp3 inflammasomes.

The innovative medicines initiative: a public private partnership model to foster drug discovery

The Innovative Medicines Initiative (IMI) is a large-scale public–private partnership between the European Commission and the European Federation of Pharmaceutical Industries and Associations (EFPIA). IMI aims to boost the development of new medicines across Europe by implementing new collaborative endeavours between large pharmaceutical companies and other key actors in the health-care ecosystem, i.e., academic institutions, small and medium enterprises, patients, and regulatory authorities. Currently there are more than 40 IMI projects covering the whole value chain of pharmaceutical R&D, but with a strong focus on drug discovery, as an ideal arena where the PPP concept of pre-competitive collaboration can rapidly deliver results. This article review recent achievements of the IMI consortia of relevance to drug discovery, providing proof-of-concept evidence for the efficiency of this new model of collaboration.

LDLR-/-ApoB100/100 mice with insulin-like growth factor II overexpression reveal a novel form of retinopathy with photoreceptor atrophy and altered morphology of the retina

PURPOSE

The aim of this study was to characterize the ocular morphology of low-density lipoprotein receptor-deficient apolipoprotein B-100-only mice, where overexpression of insulin-like growth factor II (IGF-II) has been shown to induce glucose intolerance and increase atherosclerotic lesion progression and calcification.

METHODS

Fifteen-month-old mice were examined on a normal chow diet and after 3 months of a high-fat Western diet. IGF-II-negative LDLR(-/-)ApoB(100/100) littermates and C57Bl/6J mice served as controls. In vivo color images of the fundi were obtained, and eyes were processed either for retinal flat mounts for assessment of neovascularization or for paraffin-embedded samples for immunohistochemical analyses.

RESULTS

IGF-II overexpression and the resulting prediabetic phenotype did not induce microvascular damage when assessed in fundus photographs and retinal whole mounts, and the number of capillaries in IGF-II/LDLR(-/-)ApoB(100/100) mice was not significantly different from LDLR(-/-)ApoB(100/100) mice. However, morphology of the inner nuclear, outer plexiform, and outer nuclear layers was altered in the IGF-II/LDLR(-/-)ApoB(100/100) mice. Moreover, photoreceptor atrophy and thinning of the outer nuclear layer were present. Caspase-3 staining was positive in the photoreceptor inner segment. In addition, retinas of the IGF-II/LDLR(-/-)ApoB(100/100) mice displayed reduced rhodopsin positivity, consistent with the decreased number of photoreceptor cells.

CONCLUSIONS

This study reports a novel form of retinopathy with photoreceptor atrophy and abundant changes in retinal morphology in a mouse model of prediabetes and atherosclerosis.

Promoting blood vessel growth in ischemic diseases: challenges in translating preclinical potential into clinical success

Angiogenic therapy, which involves the use of an exogenous stimulus to promote blood vessel growth, is an attractive approach for the treatment of ischemic diseases. It has been shown in animal models that the stimulation of blood vessel growth leads to the growth of the whole vascular tree, improvement of ischemic tissue perfusion and improved muscle aerobic energy metabolism. However, very few positive results have been gained from Phase 2 and 3 clinical angiogenesis trials. Many reasons have been given for the failures of clinical trials, including poor transgene expression (in gene-therapy trials) and instability of the vessels induced by therapy. In this Review, we discuss the selection of preclinical models as one of the main reasons why clinical translation has been unsuccessful thus far. This issue has received little attention, but could have had dramatic implications on the expectations of clinical trials. We highlight crucial differences between human patients and animal models with regards to blood flow and pressure, as well as issues concerning the chronic nature of ischemic diseases in humans. We use these as examples to demonstrate why the results from preclinical trials might have overestimated the efficacy of angiogenic therapies developed to date. We also suggest ways in which currently available animal models of ischemic disease could be improved to better mimic human disease conditions, and offer advice on how to work with existing models to avoid overestimating the efficacy of new angiogenic therapies.

Hyperglycemia in apolipoprotein E-deficient mouse strains with different atherosclerosis susceptibility

Background

Type 2 diabetes mellitus (T2DM) is associated with an increased risk of atherosclerotic vascular disease, but it is unknown whether the other way around is true too. C57BL/6 (B6) and BALB/cJ (BALB) are two mouse strains that differ markedly in their susceptibility to atherosclerosis. In this study we investigated the development of diet-induced T2DM in these two strains.

Methods and Results

When deficient in apolipoprotein E (apoE^-/-) and fed a Western diet for 12 weeks, atherosclerosis-susceptible B6 mice developed significant hyperglycemia. In contrast, atherosclerosis-resistant BALB apoE^-/- mice had much lower plasma glucose levels than B6.apoE^-/- mice on either chow or Western diet and during an intraperitoneal glucose tolerance test. In response to glucose BALB.apoE^-/- mice displayed both the first and second phases of insulin secretion but the second phase of insulin secretion was absent in B6.apoE^-/- mice. In response to insulin B6.apoE^-/- mice showed a deeper and longer-lasting fall in blood glucose levels while BALB.apoE^-/- mice showed little reduction in glucose levels. Pancreatic islet area of BALB.apoE^-/- mice on light microscopy nearly doubled the area of B6.apoE^-/- mice. Most circulating proinflammatory cytokines were lower in BALB.apoE^-/- than in B6.apoE^-/- mice on the Western diet, as determined by protein arrays. Increased macrophage infiltration in islets was observed in B6.apoE^-/- mice by immunostaining for Mac2 and also by flow cytometry.

Conclusion

This study demonstrates that defects in insulin secretion rather than defects in insulin resistance explain the marketed difference in susceptibility to T2DM in the B6.apoE^-/- and BALB.apoE^-/- mouse model. A smaller islet mass and more prominent islet inflammation may explain the vulnerability of B6.apoE^-/- mice to diet-induced diabetes.