Nephropathy in a Hypercholesterolemic Mouse Model with Streptozotocin-Induced Diabetes

Novel Nongenetic Murine Model of Hyperglycemia and Hyperlipidemia-Associated Aggravated Atherosclerosis

Objective

Atherosclerosis, the main pathology underlying cardiovascular diseases is accelerated in diabetic patients. Genetic mouse models require breeding efforts which are time-consuming and costly. Our aim was to establish a new nongenetic model of inducible metabolic risk factors that mimics hyperlipidemia, hyperglycemia, or both and allows the detection of phenotypic differences dependent on the metabolic stressor(s).

Methods and Results

Wild-type mice were injected with gain-of-function PCSK9D377Y (proprotein convertase subtilisin/kexin type 9) mutant adeno-associated viral particles (AAV) and streptozotocin and fed either a high-fat diet (HFD) for 12 or 20 weeks or a high-cholesterol/high-fat diet (Paigen diet, PD) for 8 weeks. To evaluate atherosclerosis, two different vascular sites (aortic sinus and the truncus of the brachiocephalic artery) were examined in the mice. Combined hyperlipidemic and hyperglycemic (HGHCi) mice fed a HFD or PD displayed characteristic features of aggravated atherosclerosis when compared to hyperlipidemia (HCi HFD or PD) mice alone. Atherosclerotic plaques of HGHCi HFD animals were larger, showed a less stable phenotype (measured by the increased necrotic core area, reduced fibrous cap thickness, and less α-SMA-positive area) and had more inflammation (increased plasma IL-1β level, aortic pro-inflammatory gene expression, and MOMA-2-positive cells in the BCA) after 20 weeks of HFD. Differences between the HGHCi and HCi HFD models were confirmed using RNA-seq analysis of aortic tissue, revealing that significantly more genes were dysregulated in mice with combined hyperlipidemia and hyperglycemia than in the hyperlipidemia-only group. The HGHCi-associated genes were related to pathways regulating inflammation (increased Cd68, iNos, and Tnfa expression) and extracellular matrix degradation (Adamts4 and Mmp14). When comparing HFD with PD, the PD aggravated atherosclerosis to a greater extent in mice and showed plaque formation after 8 weeks. Hyperlipidemic and hyperglycemic mice fed a PD (HGHCi PD) showed less collagen (Sirius red) and increased inflammation (CD68-positive cells) within aortic plaques than hyperlipidemic mice (HCi PD). HGHCi-PD mice represent a directly inducible hyperglycemic atherosclerosis model compared with HFD-fed mice, in which atherosclerosis is severe by 8 weeks.

Conclusion

We established a nongenetically inducible mouse model allowing comparative analyses of atherosclerosis in HCi and HGHCi conditions and its modification by diet, allowing analyses of multiple metabolic hits in mice.

Disparate Effects of Diabetes and Hyperlipidemia on Experimental Kidney Disease

It is well established that diabetes is the major cause of chronic kidney disease worldwide. Both hyperglycemia, and more recently, advanced glycation endproducts, have been shown to play critical roles in the development of kidney disease. Moreover, the renin-angiotensin system along with growth factors and cytokines have also been shown to contribute to the onset and progression of diabetic kidney disease; however, the role of lipids in this context is poorly characterized. The current study aimed to compare the effect of 20 weeks of streptozotocin-induced diabetes or western diet feeding on kidney disease in two different mouse strains, C57BL/6 mice and hyperlipidemic apolipoprotein (apo) E knockout (KO) mice. Mice were fed a chow diet (control), a western diet (21% fat, 0.15% cholesterol) or were induced with streptozotocin-diabetes (55 mg/kg/day for 5 days) then fed a chow diet and followed for 20 weeks. The induction of diabetes was associated with a 3-fold elevation in glycated hemoglobin and an increase in kidney to body weight ratio regardless of strain (p < 0.0001). ApoE deficiency significantly increased plasma cholesterol and triglyceride levels and feeding of a western diet exacerbated these effects. Despite this, urinary albumin excretion (UAE) was elevated in diabetic mice to a similar extent in both strains (p < 0.0001) but no effect was seen with a western diet in either strain. Diabetes was also associated with extracellular matrix accumulation in both strains, and western diet feeding to a lesser extent in apoE KO mice. Consistent with this, an increase in renal mRNA expression of the fibrotic marker, fibronectin, was observed in diabetic C57BL/6 mice (p < 0.0001). In summary, these studies demonstrate disparate effects of diabetes and hyperlipidemia on kidney injury, with features of the diabetic milieu other than lipids suggested to play a more prominent role in driving renal pathology.

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.

Circulating cholesterol as a modulator of risk for renal injury in patients with type 2 diabetes

Amelioration of albuminuria may be related to specific constellations of risk factors including race and dyslipidaemia. Circulating cholesterol could mitigate the beneficial effect of antihypertensive therapy. We assessed whether cholesterol affected the remission of urinary albumin in patients with type 2 diabetes of white, Caucasian and non-white origin. We studied 100 patients (African and Asian: n=57 and Caucasian: n=43) with type 2 diabetes and newly diagnosed microalbuminuria who received intensified and structured care for a median (IQ range) of 41 (32-48) months. Microalbuminuria remitted in 20% and progressed in 12% of patients. In those with uncontrolled systolic hypertension (>140 mmHg) systolic blood pressure fell by a mean (95% CI) of -9.4 (-3.8 to -15.11)mmHg; p=0.002. The change in urinary albumin excretion with time varied inversely with baseline systolic blood pressure (r=-0.25; p=0.04). At 3 years follow-up the decrement in blood pressure was significant for those patients in the regression group (-19.6[16.8]mmHg; p=0.005). In patients of African origin, systolic blood pressure was higher than in the other groups and correlated with cholesterol concentrations (r=0.44; p=0.04). Baseline systolic blood pressure and total cholesterol (odds ratio [95%CI]) were independent determinants of remission and progression of microalbuminuria (1.04[1.006-1.064]; p=0.02 and 1.75[1.03-2.95]; p=0.04). Patients with higher total cholesterol and baseline urinary albumin excretion were less likely to go into remission. Blood pressure correlated with cholesterol concentrations in patients of African origin. Specific cholesterol lowering strategies may benefit certain patients groups at high risk of renal disease.

Factores que influyen en la aparición de la nefropatía diabética incipiente: estudio ESODIAH

BACKGROUND AND OBJECTIVE

High cholesterol levels might contribute to the presence of albuminuria. The objective of our study was to evaluate the influence of lipid levels on the development of incipient diabetic nephropathy. Secondary objectives were to evaluate the effects of diabetes control, high blood pressure, age, sex, years of diabetes evolution, body mass index and smoking.

PATIENTS AND METHOD

930 subjects were enrolled in an open observational prospective cohort study of subjects with type 2 diabetes mellitus and high cholesterol levels (ESODIAH study) for 2 years. In our nephropathy study we selected 590 patients who had albuminuria measurements done. In every 4-month interval visit we made a clinical evaluation and blood analysis including HbA1c, lipid profile and microalbuminuria. Statistical analysis included t-Student, chi2 test, and binary logistic regressions.

RESULTS

51.7% men, aged 62.08 years of age and with an evolution of their diabetes of 8.49 years were studied. 40.6% had microalbuminuria and 59.4% had normoalbuminuria. High HbA1c correlated with the presence of albuminuria (odds ratio [OR] = 1.3; 95% confidence interval [CI], 1.12-1.55; p = 0.001). The development of microalbuminuria was more frequent in younger (OR = 0.93; 95% CI, 0.89-0.98), smoker (OR = 3.19; 95% CI, 1.02-9.96), subjects with high systolic blood pressure (OR = 1.02; 95% CI, 1-1.05). Total cholesterol levels at the end of the study were higher in new microalbuminuric (group I) than normoalbuminuric patients (group II) (group I: 211.08 [34.75] mg/dl vs group II: 200.67 [30.50]; p = 0.042).

CONCLUSIONS

Tobacco, blood pressure and diabetes control influences the presence and development of microalbuminuria. More studies are required to study the influence of hypercholesterolemia.

Diabetic nephropathy: of mice and men

Accumulating evidence supports intrinsic genetic susceptibility as an important variable in the progression of diabetic nephropathy in people. Mice provide an experimental platform of unparalleled power for dissecting the genetics of mammalian diseases; however, phenotypic analysis of diabetic mice lags behind that already established for humans. Standardized benchmarks of hyperglycemia, albuminuria, and measurements of renal failure remain to be developed for different inbred strains of mice. The most glaring deficiency has been the lack of a diabetic mouse model that develops progressively worsening renal insufficiency, the sine qua non of diabetic nephropathy in humans. Differences in susceptibility of these inbred strains to complications of diabetes mellitus provide a possible avenue to dissect the genetic basis of diabetic nephropathy; however, the identification of those strains and/or mutants most susceptible to renal injury from diabetes mellitus is lacking. Identification of a mouse model that faithfully mirrors the pathogenesis of DN in humans will undoubtedly facilitate the development of new diagnostic and therapeutic interventions.

High-dose thiamine therapy counters dyslipidaemia in streptozotocin-induced diabetic rats

AIMS/HYPOTHESIS

Cardiovascular disease in diabetes is linked to increased risk of atherosclerosis, increased levels of triglyceride-rich lipoproteins and enhanced hepatic lipogenesis. The hepatic hexosamine pathway has been implicated in signalling for de novo lipogenesis by the liver. In this study, we assessed if decrease of flux through the hexosamine pathway induced by high-dose thiamine therapy counters diabetic dyslipidaemia.

METHODS

The model of diabetes used was the streptozotocin-induced diabetic rat with maintenance insulin therapy. Normal control and diabetic rats were studied for 24 weeks with and without oral high-dose therapy (7 and 70 mg/kg) with thiamine and benfotiamine. Plasma total cholesterol, HDL cholesterol and triglycerides were determined at 6-week intervals and hepatic metabolites and transketolase activity after death of the rats at 24 weeks.

RESULTS

We found that thiamine therapy (70 mg/kg) prevented diabetes-induced increases in plasma cholesterol and triglycerides in diabetic rats but did not reverse the diabetes-induced decrease of HDL. This was achieved by prevention of thiamine depletion and decreased transketolase activity in the liver of diabetic rats. There was a concomitant decrease in hepatic UDP-N-acetylglucosamine and fatty acid synthase activity. Thiamine also normalised food intake of diabetic rats. A lower dose of thiamine (7 mg/kg) and the thiamine monophosphate prodrug benfotiamine (7 and 70 mg/kg) were ineffective.

CONCLUSIONS/INTERPRETATION

High-dose thiamine therapy prevented diabetic dyslipidaemia in experimental diabetes probably by suppression of food intake and hexosamine pathway signalling but other factors may also be involved. Benfotiamine was ineffective.

Mouse models of diabetic nephropathy

Mice provide an experimental model of unparalleled flexibility for studying mammalian diseases. Inbred strains of mice exhibit substantial differences in their susceptibility to the renal complications of diabetes. Much remains to be established regarding the course of diabetic nephropathy (DN) in mice as well as defining those strains and/or mutants that are most susceptible to renal injury from diabetes. Through the use of the unique genetic reagents available in mice (including knockouts and transgenics), the validation of a mouse model reproducing human DN should significantly facilitate the understanding of the underlying genetic mechanisms that contribute to the development of DN. Establishment of an authentic mouse model of DN will undoubtedly facilitate testing of translational diagnostic and therapeutic interventions in mice before testing in humans.

A novel in vivo lecithin-cholesterol acyltransferase (LCAT)-deficient mouse expressing predominantly LpX is associated with spontaneous glomerulopathy

Complete lecithin cholesterol acyltransferase (LCAT) deficiency is a rare genetic cause of extreme reduction in high density lipoproteins and there is a high prevalence of chronic renal dysfunction that may progress to renal failure. Previous in vitro studies suggest the vesicular lipoprotein X (LpX) particles commonly seen in LCAT-deficient plasmas may be causative. To test this hypothesis, we have generated a novel murine model that selectively accumulate LpX in the circulation by cross breeding the sterol regulatory element binding protein (SREBP) 1a transgenic mice (S+) with the LCAT knockout (lcat-/-) mice. Fast protein liquid chromatography fractionation of pooled plasma lipids revealed that virtually all cholesterol is concentrated in the very low density lipoprotein (VLDL)-sized fractions. These fractions are enriched in free cholesterol and phospholipid but extremely poor in triglyceride. Electron microscopy of the d <1.063 g/ml fraction of the S+lcat-/- mice revealed abnormal large vesicular particles, suggestive of LpX. The S+lcat-/- mice developed glomerular lesions spontaneously evident at 6 months with glomerular and tubulointerstitial lipid-deposits. Immunohistochemical staining with RhoA showed marked positive focal staining in glomeruli in the S+lcat-/- mice and undetectable in the S+/lcat+/+ control. By 10 months of age, the kidneys showed progressive glomerular injury including segmental foam cell infiltrates, mesangial expansion, and hyalinosis. Renal abnormalities are very similar to those seen in human LCAT deficiency. We conclude that the selective high-level accumulation of plasma LpX in the S+lcat-/- mice is strongly associated with a spontaneous glomerulopathy, providing in vivo evidence that LpX contributes to the LCAT deficiency-related nephropathy.