Endocrine and Metabolic Effects of Consuming Sugar-Sweetened Beverages: Preclinical and Clinical Studies

Peter J. Havel of the School of Veterinary Medicine at UC Davis will speak on his research on Endocrine and Metabolic Effects of Consuming Sugar-Sweetened Beverages: Preclinical and clinical studies at this Science Seminar Series lecture

Endocrine and Metabolic Effects of Consuming Sugar-Sweetened Beverages: Preclinical and Clinical Studies

Peter J. Havel of the School of Veterinary Medicine at UC Davis will speak on his research on Endocrine and Metabolic Effects of Consuming Sugar-Sweetened Beverages: Preclinical and clinical studies at this Science Seminar Series lecture

Role of angiopoietin-like protein 3 in sugar-induced dyslipidemia in rhesus macaques: suppression by fish oil or RNAi.

Angiopoietin-like protein 3 (ANGPTL3) inhibits lipid clearance and is a promising target for managing cardiovascular disease. Here we investigated the effects of a high-sugar (high-fructose) diet on circulating ANGPTL3 concentrations in rhesus macaques. Plasma ANGPTL3 concentrations increased ∼30% to 40% after 1 and 3 months of a high-fructose diet (both P < 0.001 vs. baseline). During fructose-induced metabolic dysregulation, plasma ANGPTL3 concentrations were positively correlated with circulating indices of insulin resistance [assessed with fasting insulin and the homeostatic model assessment of insulin resistance (HOMA-IR)], hypertriglyceridemia, adiposity (assessed as leptin), and systemic inflammation [C-reactive peptide (CRP)] and negatively correlated with plasma levels of the insulin-sensitizing hormone adropin. Multiple regression analyses identified a strong association between circulating APOC3 and ANGPTL3 concentrations. Higher baseline plasma levels of both ANGPTL3 and APOC3 were associated with an increased risk for fructose-induced insulin resistance. Fish oil previously shown to prevent insulin resistance and hypertriglyceridemia in this model prevented increases of ANGPTL3 without affecting systemic inflammation (increased plasma CRP and interleukin-6 concentrations). ANGPTL3 RNAi lowered plasma concentrations of ANGPTL3, triglycerides (TGs), VLDL-C, APOC3, and APOE. These decreases were consistent with a reduced risk of atherosclerosis. In summary, dietary sugar-induced increases of circulating ANGPTL3 concentrations after metabolic dysregulation correlated positively with leptin levels, HOMA-IR, and dyslipidemia. Targeting ANGPTL3 expression with RNAi inhibited dyslipidemia by lowering plasma TGs, VLDL-C, APOC3, and APOE levels in rhesus macaques

Trabecular and Cortical Bone and Ossified Vessel Alterations in Rat Tibiae with the Onset and Progression of Type 2 Diabetes Mellitus in a Novel, Transgenic Rat Model

Type 2 Diabetes Mellitus (T2DM) is a metabolic disorder of systemic complications including increased fracture risk and microvascular pathology, suggesting a potential link between the two. PURPOSE: We determined how the onset and progression of T2DM affected bone and marrow vasculature in the University of California Davis T2DM transgenic rat model. METHODS: Forty-eight male T2DM rats were divided accordingly: pre-diabetes (12wks), diabetes onset (14wks), early-stage diabetes (20wks; 4wks post-onset), and late-stage diabetes (22wks; 12wks post-onset) matched with four healthy control (CTL; Sprague Dawley) groups. Body mass(g), HbA1c(%), and fasted blood glucose(g/dL) were measured at sacrifice. Tibiae were scanned via µCT (15µm) to assess trabecular volume-to-total volume ratio (BV/TV, %), trabecular thickness (Tb.Th, µm), trabecular number (Tb.N, /mm), trabecular separation (Tb.Sp µm), and density (mgHA/ccm) in the proximal metaphysis. Cortical thickness (Ct.Th, µm) and density (mmHg/ccm) were measured at the mid-shaft, and cortical porosity (%) was calculated (1-Ct.BV/TV). Ossified vessel volume (OsVV, %), ossified vessel thickness (OsV.Th, µm), and OsV density (mgHA/ccm) were analyzed in the diaphyseal marrow, representing conversion of blood vessels into bone-like tissue. A General Linear Model determined significance at p\u3c0.05, a priori. RESULTS: Body mass (455-622g vs. 342-435g) and HbA1c (5-12% vs. 5%) was higher (p\u3c0.05) in the T2DM vs. CTL groups, respectively. Blood glucose rose (p\u3c0.05) in early- (113±9g/dL vs. 71±7g/dL) and late- (244±10g/dL vs. 68±2g/dL) stage diabetes vs. CTL. Trabecular BV/TV was lower (p\u3c0.05) in pre- (4±1% vs. 9±2%) and late-stage (5±2% vs. 8±2%) diabetes vs. CTL, from reduced (p\u3c0.05) Tb.N in pre- (2.5±0.1/mm vs. CTL, 3.8±0.2/mm) and late-stage (2.1±0.3/mm vs. CTL, 2.6±0.4/mm), and reduced (p\u3c0.05) Tb.Th in late-stage (56±3µm vs. CTL, 67±4µm) diabetes. Trabecular separation increased (p\u3c0.05) in pre-(407±23µm vs. CTL, 263±15µm) and late-stage (482±85µm vs. CTL, 406±85µm). Trabecular density and Ct.Th, density, and porosity did not differ. OsVV was lower (p\u3c0.05) in early-stage diabetes (1.7±0.2% vs. CTL, 4.7±1.5%), OsV.Th was higher (p\u3c0.05) in pre-(69±14µm vs. CTL, 56±13µm) and late-stage (80±10µm vs. CTL, 59±13µm) diabetes, and OsV density was higher (p\u3c0.05) in late-stage diabetes (918±17mgHA/ccm vs. CTL, 891±31mgHA /ccm).CONCLUSION: T2DM developed in the transgenic rat model (i.e., increases in HbA1c, and blood glucose). Cortical bone parameters were not altered. Trabecular bone declined in pre- and late-stage diabetes, via reduced trabecular number and thickness. Ossified vessels were thicker at these stages. Thus, the observed trabecular bone and vascular pathologies coincided in the tibia with the onset and progress of T2DM

17β-Estradiol Treatment Improves Acetylcholine-Induced Relaxation of Mesenteric Arteries in Ovariectomized UC Davis Type 2 Diabetes Mellitus Rats in Prediabetic State

We recently reported sex differences in mesenteric arterial function of the UC Davis type-2 diabetes mellitus (UCD-T2DM) rats as early as the prediabetic state. We reported that mesenteric arteries (MA) from prediabetic male rats exhibited a greater impairment compared to that in prediabetic females. However, when females became diabetic, they exhibited a greater vascular dysfunction than males. Thus, the aim of this study was to investigate whether the female sex hormone, estrogen preserves mesenteric arterial vasorelaxation in UCD-T2DM female rats at an early prediabetic state. Age-matched female Sprague Dawley and prediabetic (PD) UCD-T2DM rats were ovariectomized (OVX) and subcutaneously implanted with either placebo or 17β-estradiol (E2, 1.5 mg) pellets for 45 days. We assessed the contribution of endothelium-derived relaxing factors (EDRF) to acetylcholine (ACh)-induced vasorelaxation, using pharmacological inhibitors. Responses to sodium nitroprusside (SNP) and phenylephrine (PE) were also measured. Additionally, metabolic parameters and expression of some targets associated with vascular and insulin signaling were determined. We demonstrated that the responses to ACh and SNP were severely impaired in the prediabetic state (PD OVX) rats, while E2 treatment restored vasorelaxation in the PD OVX + E2. Moreover, the responses to PE was significantly enhanced in MA of PD OVX groups, regardless of placebo or E2 treatment. Overall, our data suggest that 1) the impairment of ACh responses in PD OVX rats may, in part, result from the elevated contractile responses to PE, loss of contribution of endothelium-dependent hyperpolarization (EDH) to vasorelaxation, and a decreased sensitivity of MA to nitric oxide (NO), and 2) the basis for the protective effects of E2 may be partly attributed to the elevation of the NO contribution to vasorelaxation and its interaction with MA as well as potential improvement of insulin signaling. Here, we provide the first evidence of the role of E2 in protecting MA from early vascular dysfunction in prediabetic female rats

Altering Pyrroloquinoline Quinone Nutritional Status Modulates Mitochondrial, Lipid, and Energy Metabolism in Rats

We have reported that pyrroloquinoline quinone (PQQ) improves reproduction, neonatal development, and mitochondrial function in animals by mechanisms that involve mitochondrial related cell signaling pathways. To extend these observations, the influence of PQQ on energy and lipid relationships and apparent protection against ischemia reperfusion injury are described herein. Sprague-Dawley rats were fed a nutritionally complete diet with PQQ added at either 0 (PQQ−) or 2 mg PQQ/Kg diet (PQQ+). Measurements included: 1) serum glucose and insulin, 2) total energy expenditure per metabolic body size (Wt3/4), 3) respiratory quotients (in the fed and fasted states), 4) changes in plasma lipids, 5) the relative mitochondrial amount in liver and heart, and 6) indices related to cardiac ischemia. For the latter, rats (PQQ− or PQQ+) were subjected to left anterior descending occlusions followed by 2 h of reperfusion to determine PQQ's influence on infarct size and myocardial tissue levels of malondialdehyde, an indicator of lipid peroxidation. Although no striking differences in serum glucose, insulin, and free fatty acid levels were observed, energy expenditure was lower in PQQ− vs. PQQ+ rats and energy expenditure (fed state) was correlated with the hepatic mitochondrial content. Elevations in plasma di- and triacylglyceride and β-hydroxybutryic acid concentrations were also observed in PQQ− rats vs. PQQ+ rats. Moreover, PQQ administration (i.p. at 4.5 mg/kg BW for 3 days) resulted in a greater than 2-fold decrease in plasma triglycerides during a 6-hour fast than saline administration in a rat model of type 2 diabetes. Cardiac injury resulting from ischemia/reperfusion was more pronounced in PQQ− rats than in PQQ+ rats. Collectively, these data demonstrate that PQQ deficiency impacts a number of parameters related to normal mitochondrial function

Using HbA1c to Diagnose Diabetes in the UC, Davis-Type 2 Diabetes Mellitus Rat Model

With disease progression, type 2 diabetes mellitus (T2DM) leads to debilitating complications arising from damage to nerves and blood vessels. Importantly, investigations focusing on T2DM progression have the capacity to distinguish individuals at greater risk for these severe complications through the identification of predictive biomarkers. Hence, the accurate diagnosis of T2DM is critical to such investigations. UC Davis (UCD) T2DM rats are born without diabetes and develop the disease over time with a similar pathophysiology to that in humans. This unique rat model allows researchers to investigate predictive biomarkers linked to the progression of T2D; however, such investigations require an accurate diagnosis of T2DM onset. PURPOSE: To determine the most accurate measure to diagnose T2DM using UCD-T2DM rats. METHODS: 10 male UCD-T2DM rats were used in this study. Glucose and HbA1c were measured weekly from the tail beginning at 16 wks of age (before onset) and continuing until 25 wks of age (all rats had become diabetic). These measures were taken under both fasted (8 hrs) and random conditions as well as in the morning (AM) and afternoon (PM). A two-way repeated measures ANOVA was run with condition [fasted (FG) vs random (RG)] and time (AM vs PM) as factors, followed by Holm Sidak post hoc analyses. In addition, growth curves were fit to the data for all rats to estimate the trajectories of RG and HbA1c. RESULTS: We found that RG was more variable compared to FG (FG: 116±46 vs RG: 216±94 mg/dL; n=10). However, HbA1c was stable across both conditions (fasted HbA1c: 6.0±0.8 vs random HbA1c: 6.0±1.0%; n=10). In addition, both FG and RG morning levels were significantly lower compared to afternoon (FG AM: 99±6 vs FG PM: 133±19 mg/dL; n=10; p0.05). In addition, the location on the growth curve where RG crossed 200 mg/dL (currently the most common diagnostic criteria used) corresponded to a HbA1c of 5.6%. CONCLUSION: A HbA1c of 5.6% may provide a more accurate measure to diagnose the onset of diabetes in the UCD-T2DM rat model

Potentiation of Acetylcholine-Induced Relaxation of Aorta in Male UC Davis Type 2 Diabetes Mellitus (UCD-T2DM) Rats: Sex-Specific Responses

Previous reports suggest that diabetes may differentially affect the vascular beds of females and males. The objectives of this study were to examine whether there were (1) sex differences in aortic function and (2) alterations in the relative contribution of endothelium-derived relaxing factors in modulating aortic reactivity in UC Davis Type 2 Diabetes Mellitus (UCD-T2DM) rats. Endothelium-dependent vasorelaxation (EDV) in response to acetylcholine (ACh) was measured in aortic rings before and after exposure to pharmacological inhibitors. Relaxation responses to sodium nitroprusside were assessed in endothelium-denuded rings. Moreover, contractile responses to phenylephrine (PE) were measured before and after incubation of aortic rings with a nitric oxide synthase (NOS) inhibitor in the presence of indomethacin. Metabolic parameters and expression of molecules associated with vascular and insulin signaling as well as reactive oxygen species generation were determined. Diabetes slightly but significantly impaired EDV in response to ACh in aortas from females but potentiated the relaxation response in males. The potentiation of EDV in diabetic male aortas was accompanied by a traces of nitric oxide (NO)- and prostanoid-independent relaxation and elevated aortic expression of small- and intermediate conductance Ca2+-activated K+ channels in this group. The smooth muscle sensitivity to NO was not altered, whereas the responsiveness to PE was significantly enhanced in aortas of diabetic groups in both sexes. Endothelium-derived NO during smooth muscle contraction, as assessed by the potentiation of the response to PE after NOS inhibition, was reduced in aortas of diabetic rats regardless of sex. Accordingly, decreases in pAkt and peNOS were observed in aortas from diabetic rats in both sexes compared with controls. Our data suggest that a decrease in insulin sensitivity via pAkt-peNOS-dependent signaling and an increase in oxidative stress may contribute to the elevated contractile responses observed in diabetic aortas in both sexes. This study demonstrates that aortic function in UCD-T2DM rats is altered in both sexes. Here, we provide the first evidence of sexual dimorphism in aortic relaxation in UCD-T2DM rats

Obesity Contributes to an Attenuated Spontaneous Baroreflex Sensitivity in UCD-Type 2 Diabetic Rats

Previous studies suggest impaired baroreflex function in individuals with type 2 diabetes (T2D), which is critically important since it leads to an increased risk for adverse cardiovascular events. Currently, the underlying mechanisms remain poorly understood. The baroreflex, essential for maintaining blood pressure homeostasis, can also be influenced by several risk factors, one of which is obesity. Obesity has been shown to markedly decrease baroreflex sensitivity (BRS) in non-diabetic individuals, and given that the majority of T2D patients are obese, it is likely that impairment in baroreflex function in T2D is mainly driven by obesity. PURPOSE: To investigate the effects of obesity on baroreflex function in T2D rats at different phases of the disease. We hypothesized that BRS would be attenuated in T2D rats, and this would be associated with increased adiposity. METHODS: Experiments were performed on male University of California Davis (UCD)-T2D rats assigned to four experimental groups (n=6 in each group): prediabetic (PD), diabetes-onset (DO), 4 weeks after onset [recent-onset (RO)], and 12 weeks after onset [late-onset (LO)]. Age-matched healthy Sprague-Dawley rats were assigned to the same experimental groups as controls (n=6 in each). Rats were anesthetized and blood pressure was directly measured for 5 min. Hemodynamic variables were obtained on a beat-to-beat basis and spontaneous BRS was assessed using the sequence technique. Dual-energy X-ray absorptiometry (DEXA) was used to assess body composition and visceral fat was determined by identifying an abdominal region of interest. Data are presented as mean ± SD. RESULTS: Spontaneous BRS was significantly lower in T2D compared to control rats at DO (3.7 ± 3.2 ms/mmHg vs 16.1 ± 8.4 ms/mmHg; P=0.01). However, this difference was abolished by LO (13.4 ± 8.1 ms/mmHg vs 9.2 ± 6.0 ms/mmHg; P=0.16). T2D rats had the highest level of adiposity during the RO phase but it significantly decreased by LO (PD: 136 ± 14 g; DO: 175 ± 24 g; RO: 207 ± 44 g; LO: 163 ± 45 g; P=0.03). In addition, T2D rats had greater visceral fat compared to control rats regardless of the disease phase (P\u3c0.01). CONCLUSION: These findings suggest that obesity may contribute to an attenuated spontaneous BRS in T2D rats and suggests a link between metabolic and autonomic dysfunction in T2D