Modeling diabetes disease progression and salsalate intervention in Goto-Kakizaki rats

OLED catheters for inner-body phototherapy: A case of type 2 diabetes mellitus improved via duodenal photobiomodulation

Phototherapeutics has shown promise in treating various diseases without surgical or drug interventions. However, it is challenging to use it in inner-body applications due to the limited light penetration depth through the skin. Therefore, we propose an organic light-emitting diode (OLED) catheter as an effective photobiomodulation (PBM) platform useful for tubular organs such as duodenums. A fully encapsulated highly flexible OLED is mounted over a round columnar structure, producing axially uniform illumination without local hotspots. The biocompatible and airtight OLED catheter can operate in aqueous environments for extended periods, meeting the essential requirements for inner-body medical applications. In a diabetic Goto-Kakizaki (GK) rat model, the red OLED catheter delivering 798 mJ of energy is shown to reduce hyperglycemia and insulin resistance compared to the sham group. Results are further supported by the subdued liver fibrosis, illustrating the immense potential of the OLED-catheter-based internal PBM for the treatment of type 2 diabetes and other diseases yet to be identified.

Preclinical evaluation of tolvaptan and salsalate combination therapy in a Pkd1-mouse model

Background: Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic disorder and an important cause of end stage renal disease (ESRD). Tolvaptan (a V2R antagonist) is the first disease modifier drug for treatment of ADPKD, but also causes severe polyuria. AMPK activators have been shown to attenuate cystic kidney disease. Methods: In this study, we tested the efficacy of the combined administration of salsalate (a direct AMPK activator) and tolvaptan using clinically relevant doses in an adult-onset conditional Pkd1 knock-out (KO) mouse model. Results: Compared to untreated Pkd1 mutant mice, the therapeutic effects of salsalate were similar to that of tolvaptan. The combined treatment tended to be more effective than individual drugs used alone, and was associated with improved kidney survival (p < 0.0001) and reduced kidney weight to body weight ratio (p < 0.0001), cystic index (p < 0.001) and blood urea levels (p < 0.001) compared to untreated animals, although the difference between combination and single treatments was not statistically significant. Gene expression profiling and protein expression and phosphorylation analyses support the mild beneficial effects of co-treatment, and showed that tolvaptan and salsalate cooperatively attenuated kidney injury, cell proliferation, cell cycle progression, inflammation and fibrosis, and improving mitochondrial health, and cellular antioxidant response. Conclusion: These data suggest that salsalate-tolvaptan combination, if confirmed in clinical testing, might represent a promising therapeutic strategy in the treatment of ADPKD.

Alterations in Energy Metabolism, Mitochondrial Function and Redox Homeostasis in GK Diabetic Rat Tissues Treated with Aspirin

Our recent studies have demonstrated that aspirin treatment prevents inflammatory and oxidative stress-induced alterations in mitochondrial function, improves glucose tolerance and pancreatic endocrine function and preserves tissue-specific glutathione (GSH)-dependent redox homeostasis in Goto-Kakizaki (GK) diabetic rats. In the current study, we have investigated the mechanism of action of aspirin in maintaining mitochondrial bioenergetics and redox metabolism in the liver and kidneys of GK rats. Aspirin reduced the production of reactive oxygen species (ROS) and oxidative stress-induced changes in GSH metabolism. Aspirin treatment also improved mitochondrial respiratory function and energy metabolism, in addition to regulating the expression of cell signaling proteins that were altered in diabetic animals. Ultrastructural electron microscopy studies revealed decreased accumulation of glycogen in the liver of aspirin-treated diabetic rats. Hypertrophic podocytes with irregular fusion of foot processes in the renal glomerulus and detached microvilli, condensed nuclei and degenerated mitochondria observed in the proximal convoluted tubules of GK rats were partially restored by aspirin. These results provide additional evidence to support our previous observation of moderation of diabetic complications by aspirin treatment in GK rats and may have implications for cautious use of aspirin in the therapeutic management of diabetes.

Effect of Aspirin on Mitochondrial Dysfunction and Stress in the Pancreas and Heart of Goto-Kakizaki Diabetic Rats

Our previous study in Goto-Kakizaki (GK) type 2 diabetic rats provided significant evidence that aspirin treatment improves pancreatic β-cell function by reducing inflammatory responses and improving glucose tolerance. In the present study, we aimed to elucidate the mechanism of action of aspirin on the pathophysiology and progression of type 2 diabetic complications in the heart and pancreas of insulin-resistant GK rats. Aspirin treatment demonstrated a reduction in mitochondrial reactive oxygen species (ROS) production and lipid peroxidation, accompanied by improved redox homeostasis. Furthermore, the recovery of metabolic and mitochondrial functions, as well as cytochrome P450 enzyme activities, which were altered in the pancreas and heart of GK rats, were observed. Aspirin treatment brought the activity of CYP 2E1 to the control level in both tissues, whereas the CYP 3A4 level decreased only in the pancreas. This suggests the tissue-specific differential metabolism of substrates in these rats. The recovery of redox homeostasis could be the key target in the improvement of oxidative-stress-dependent alterations in mitochondrial functions which, in turn, facilitated improved energy metabolism in these tissues in the aspirin-treated GK rats. These results may have implications in determining the therapeutic use of aspirin, either alone or in combination with other clinically approved therapies, in insulin-resistant type 2 diabetes.

Attenuation of diabetic cardiomyopathy by relying on kirenol to suppress inflammation in a diabetic rat model

Diabetic cardiomyopathy is characterized by diabetes‐induced myocardial abnormalities, accompanied by inflammatory response and alterations in inflammation‐related signalling pathways. Kirenol, isolated from Herba Siegesbeckiae, has potent anti‐inflammatory properties. In this study, we aimed to investigate the cardioprotective effect of kirenol against DCM and underlying the potential mechanisms in a type 2 diabetes mellitus model. Kirenol treatment significantly decreased high glucose‐induced cardiofibroblasts proliferation and increased the cardiomyocytes viability, prevented the loss of mitochondrial membrane potential and further attenuated cardiomyocytes apoptosis, accompanied by a reduction in apoptosis‐related protein expression. Kirenol gavage could affect the expression of pro‐inflammatory cytokines in a dose‐dependent manner but not lower lipid profiles, and only decrease fasting plasma glucose, fasting plasma insulin and mean HbA1c levels in high‐dose kirenol‐treated group at some time‐points. Left ventricular dysfunction, hypertrophy, fibrosis and cell apoptosis, as structural and functional abnormalities, were ameliorated by kirenol administration. Moreover, in diabetic hearts, oral kirenol significantly attenuated activation of mitogen‐activated protein kinase subfamily and nuclear translocation of NF‐κB and Smad2/3 and decreased phosphorylation of IκBα and both fibrosis‐related and apoptosis‐related proteins. In an Electrophoretic mobility shift assay, the binding activities of NF‐κB, Smad3/4, SP1 and AP‐1 in the nucleus of diabetic myocardium were significantly down‐regulated by kirenol treatment. Additionally, high dose significantly enhanced myocardial Akt phosphorylation without intraperitoneal injection of insulin. Kirenol may have potent cardioprotective effects on treating for the established diabetic cardiomyopathy, which involves the inhibition of inflammation and fibrosis‐related signalling pathways and is independent of lowering hyperglycaemia, hyperinsulinemia and lipid profiles.

Salsalate Activates Skeletal Muscle Thermogenesis and Protects Mice from High-Fat Diet Induced Metabolic Dysfunction

Salsalate plays beneficial roles for ameliorating hyperglycemia and dyslipidemia in type 2 diabetes patients, but the underlying mechanisms are still poorly understood. In this study, by administering salsalate to mice fed with high fat diet and examining how salsalate rectifies metabolic dysfunction in these obese mice, we found that salsalate stimulated body temperature and attenuated body weight gain without affecting food intake. Our results showed that salsalate application decreased lipid accumulation in liver and epididymal white adipose tissue (eWAT), inhibited hepatic gluconeogenesis and improved insulin signaling transduction in eWAT. In addition, salsalate increased the expression of genes related to glucose and fatty acid transport and oxidation in skeletal muscle. Our results also showed that expression of genes in mitochondrial uncoupling and mitochondrial electron transport are strengthened by salsalate. Moreover, sarcolipin (Sln) and sarcoplasmic reticulum Ca^2 + ATPase 2 (Serca2) in skeletal muscle were enhanced in salsalate-treated mice. Together, our data suggest that the beneficial metabolic effects of salsalate may depend, at least in part, on skeletal muscle thermogenesis via activation of mitochondrial uncoupling and the axis of Sln/Serca2a.

•

Salsalate improves metabolic dysfunction in high-fat diet induced obese mice.

•

Salsalate stimulates energy expenditure by activating skeletal muscle thermogenesis.

It has been well documented that salicylate-based compounds play beneficial roles for treating obesity-related metabolic syndromes and enhanced energy expenditure was thought to be one of the underlying mechanisms. However, the tissues targeted by salicylate for energy expenditure and the involved mechanisms are still not clear. Our data show that, by activating mitochondrial uncoupling and the axis of Sln/Serca2, salsalate stimulates skeletal muscle thermogenesis in high-fat diet induced obese mice. Therefore, we suggest skeletal muscle thermogenesis may account for salsalate-induced energy expenditure and its beneficial metabolic effects in type 2 diabetes patients.

A mini-network balance model for evaluating the progression of cardiovascular complications in Goto-Kakizaki rats

Cardiovascular complications represent a leading cause of mortality in patients with type 2 diabetes mellitus (T2DM). During such complicated progression, subtle variations in the cardiovascular risk (CVR)-related biomarkers have been used to identify cardiovascular disease at the incipient stage. In this study we attempt to integrally characterize the progression of cardiovascular complications and to assess the beneficial effects of metformin combined with salvianolic acid A (Sal A), in Goto-Kakizaki (GK) rats with spontaneous T2DM. The rats were treated with metformin (200 mg·kg^-1·d^-1, ig) alone or in combination with Sal A (1 mg·kg^-1·d^-1, ip) at ages from 8 to 22 weeks. During the treatment, the levels of asymmetric dimethylarginine, L-arginine, superoxide dismutase, malondialdehyde, glucose, high density lipoprotein and low density lipoprotein were assessed. Based on alterations in these biomarkers, a mini-network balance model was established using matrixes and vectors. Radar charts were created to visually depict the disruption of CVR-related modules (endothelial function, oxidative stress, glycation and lipid profiles). The description for the progression of cardiovascular disorder was quantitatively represented by u, the dynamic parameter of the model. The modeling results suggested that untreated GK rats tended to have more severe cardiovascular complications than the treatment groups. Metformin monotherapy retarded disease deterioration, whereas the combination treatment ameliorated the disease progression via restoring the balance. The current study, which focused on the balance of the mini-network and interactions among CVR-related modules, proposes a novel method for evaluating the progression of cardiovascular complications in T2DM as well as a more beneficial intervention strategy.

The effect of hyperglycaemia on osseointegration: a review of animal models of diabetes mellitus and titanium implant placement

Patients with type 2 diabetes mellitus have a higher risk of dental and/or orthopaedic implant failure. However, the mechanism behind this phenomenon is unclear, and animal studies may prove useful in shedding light on the processes involved. This review considers the available literature on rat models of diabetes and titanium implantation.

INTRODUCTION

The process of osseointegration whereby direct contact is achieved between bone and an implant surface depends on healthy bone metabolism. Collective evidence suggests that hyperglycaemia adversely affects bone turnover and the quality of the organic matrix resulting in an overall deterioration in the quality, resilience and structure of the bone tissue. This in turn results in compromised osseointegration in patients receiving dental and orthopaedic implants. The incidence of diabetes mellitus (DM), which is a chronic metabolic disorder resulting in hyperglycaemia, is rising. Of particular significance is the rising incidence of adult onset type 2 diabetes mellitus (T2DM) in an ageing population. Understanding the effects of hyperglycaemia on osseointegration will enable clinicians to manage health outcomes for patients receiving implants. Much of our understanding of how hyperglycaemia affects osseointegration comes from animal studies.

METHODS

In this review, we critically analyse the current animal studies.

RESULTS

Our review has found that most studies used a type 1 diabetes mellitus (T1DM) rodent model and looked at a young male population of rodents. The pathophysiology of T1DM is however very different to that of T2DM and is not representative of T2DM, the incidence of which is rising in the ageing adult population. Genetically modified rats have been used to model T2DM, but none of these studies have included female rats and the metabolic changes in bone for some of these models used are not adequately characterized.

CONCLUSIONS

Therefore, the review suggests that the study population needs to be broadened to include both T1DM and T2DM models, older rats as well as young rats, and importantly animals from both sexes to reflect more accurately clinical practice.

Modeling Disease Progression: Angiotensin II Indirectly Inhibits Nitric Oxide Production via ADMA Accumulation in Spontaneously Hypertensive Rats

Nitric oxide (NO) production impairment is involved in the onset and development of hypertension. Although NO production impairment in spontaneously hypertensive rat (SHR) has been reported in a variety of researches, the time course of this progressive procedure, as well as its relationship with asymmetric dimethylarginine (ADMA) and angiotensin II (Ang II), has not been quantified. The aim of this research is to establish a mechanism-based disease progression model to assess Ang II and ADMA's inhibition of NO production in SHR's disease progression with/without ramipril's intervention. SHR were randomly divided into three groups: one disease group (n = 8) and two treatment groups (n = 8 for each group): standard treatment group (receiving ramipril 2 mg/kg^*day) and intensive treatment group (receiving ramipril 10 mg/kg^*day). ADMA, Ang II, NO, and SBP were determined weekly. Intensive treatment with ramipril was found to have no further attenuation of plasma NO and ADMA than standard treatment beyond its significantly stronger antihypertensive effects. Four linked turnover models were developed to characterize the profiles of ADMA, Ang II, NO, and SBP during hypertensive disease progression with/without ramipril intervention. Our model described Ang II and ADMA's contribution to NO production impairment and their responses to ramipril treatment throughout the disease progression in SHR. Model simulations suggested that Ang II affected NO production mainly through inhibiting ADMA elimination rather than affecting nitric oxide synthase (NOS) directly.

Salsalate (Salicylate) Uncouples Mitochondria, Improves Glucose Homeostasis, and Reduces Liver Lipids Independent of AMPK-β1

Salsalate is a prodrug of salicylate that lowers blood glucose in patients with type 2 diabetes (T2D) and reduces nonalcoholic fatty liver disease (NAFLD) in animal models; however, the mechanism mediating these effects is unclear. Salicylate directly activates AMPK via the β1 subunit, but whether salsalate requires AMPK-β1 to improve T2D and NAFLD has not been examined. Therefore, wild-type (WT) and AMPK-β1-knockout (AMPK-β1KO) mice were treated with a salsalate dose resulting in clinically relevant serum salicylate concentrations (∼1 mmol/L). Salsalate treatment increased VO₂, lowered fasting glucose, improved glucose tolerance, and led to an ∼55% reduction in liver lipid content. These effects were observed in both WT and AMPK-β1KO mice. To explain these AMPK-independent effects, we found that salicylate increases oligomycin-insensitive respiration (state 4o) and directly increases mitochondrial proton conductance at clinical concentrations. This uncoupling effect is tightly correlated with the suppression of de novo lipogenesis. Salicylate is also able to stimulate brown adipose tissue respiration independent of uncoupling protein 1. These data indicate that the primary mechanism by which salsalate improves glucose homeostasis and NAFLD is via salicylate-driven mitochondrial uncoupling.

Effects of High Fat Feeding on Adipose Tissue Gene Expression in Diabetic Goto-Kakizaki Rats

Development and progression of type 2 diabetes is a complex interaction between genetics and environmental influences. High dietary fat is one environmental factor that is conducive to the development of insulin-resistant diabetes. In the present report, we compare the responses of lean poly-genic, diabetic Goto-Kakizaki (GK) rats to those of control Wistar-Kyoto (WKY) rats fed a high fat diet from weaning to 20 weeks of age. This comparison included a wide array of physiological measurements along with gene expression profiling of abdominal adipose tissue using Affymetrix gene array chips. Animals of both strains fed a high fat diet or a normal diet were sacrificed at 4, 8, 12, 16, and 20 weeks for this comparison. The microarray analysis revealed that the two strains developed different adaptations to increased dietary fat. WKY rats decrease fatty acid synthesis and lipogenic processes whereas GK rats increase lipid elimination. However, on both diets the major differences between the two strains remained essentially the same. Specifically relative to the WKY strain, the GK strain showed lipoatrophy, chronic inflammation, and insulin resistance.

Salsalate activates brown adipose tissue in mice

Salsalate improves glucose intolerance and dyslipidemia in type 2 diabetes patients, but the mechanism is still unknown. The aim of the current study was to unravel the molecular mechanisms involved in these beneficial metabolic effects of salsalate by treating mice with salsalate during and after development of high-fat diet-induced obesity. We found that salsalate attenuated and reversed high-fat diet-induced weight gain, in particular fat mass accumulation, improved glucose tolerance, and lowered plasma triglyceride levels. Mechanistically, salsalate selectively promoted the uptake of fatty acids from glycerol tri[(3)H]oleate-labeled lipoprotein-like emulsion particles by brown adipose tissue (BAT), decreased the intracellular lipid content in BAT, and increased rectal temperature, all pointing to more active BAT. The treatment of differentiated T37i brown adipocytes with salsalate increased uncoupled respiration. Moreover, salsalate upregulated Ucp1 expression and enhanced glycerol release, a dual effect that was abolished by the inhibition of cAMP-dependent protein kinase (PKA). In conclusion, salsalate activates BAT, presumably by directly activating brown adipocytes via the PKA pathway, suggesting a novel mechanism that may explain its beneficial metabolic effects in type 2 diabetes patients.

Variability in Zucker diabetic fatty rats: differences in disease progression in hyperglycemic and normoglycemic animals

Both obesity and chronic inflammation are often associated with insulin resistance and type 2 diabetes. The Zucker diabetic fatty (ZDF) rat (fa/fa) is an obese animal model frequently used in type 2 diabetes research. The current study determines whether chronic administration (from 5 weeks of age through 24 weeks of age) of salsalate, a salicylate with anti-inflammatory properties, would be effective in mitigating diabetes disease progression in ZDF rats. Although a trend existed for lower blood glucose in the salsalate-treated group, significant differences were obscured by high animal-level variability. However, even in the non-drug-treated group, not all ZDF rats became diabetic as expected. Therefore, animals were parsed into two groups, regardless of drug treatment: normoglycemic ZDF rats, which maintained blood glucose profiles identical to nondiabetic Zucker lean rats (ZLRs), and hyperglycemic ZDF rats, which exhibited progressive elevation in blood glucose. To ascertain the differences between ZDF rats that became hyperglycemic and those that did not, relevant physiological indices and expression levels of adiponectin, tumor necrosis factor-α, interleukin-6, and glucocorticoid-induced leucine zipper messenger RNAs in adipose tissue were measured at sacrifice. Plasma C-reactive protein concentrations and expression levels of cytokine and glucocorticoid-induced leucine zipper messenger RNAs suggested more prevalent chronic inflammation in hyperglycemic animals. Early elevation of the insulin-sensitizing adipokine, adiponectin, was present in both ZDF groups, with the rate of its age-related decline faster in hyperglycemic animals. The most marked difference between the two groups of ZDF animals was in insulin output. Although the two ZDF populations had very similar elevated plasma insulin concentrations for the first 10 weeks, after that time, plasma insulin decreased markedly in the animals that became hyperglycemic, whereas it remained high in the normoglycemic ZDF rats. Thus, hyperglycemic ZDF animals exhibit both insulin resistance and progressive beta cell failure, whereas normoglycemic ZDF rats exhibit a lesser degree of insulin resistance that does not progress to beta cell failure. In these respects, the normoglycemic ZDF rats appear to revert back to a phenotype that strongly resembles that of nondiabetic Zucker fatty rats from which they were derived.

The effect of duodenojejunostomy and sleeve gastrectomy on type 2 diabetes mellitus and gastrin secretion in Goto-Kakizaki rats

BACKGROUND

Bariatric surgery is a highly effective treatment of type 2 diabetes in patients with morbid obesity. The weight-loss independent improvement of glycemic control observed after these procedures has led to the discussion whether bariatric surgery can be introduced as treatment for type 2 diabetes in patients with a body mass index < 35 kg/m(2). We have studied the effects of two bariatric procedures on type 2 diabetes and on gastrointestinal hormone secretion in a lean diabetic animal model.

METHODS

Male Goto-Kakizaki rats, 17-18 weeks old, were randomized into three groups: duodenojejunostomy (DJ), sleeve gastrectomy (SG), or sham operation. During 36 postoperative weeks we evaluated body weight, fasting blood glucose, glucose tolerance, insulin, HbA1c, glucagon-like peptide 1, cholesterol parameters, triglycerides, total ghrelin, and gastrin.

RESULTS

Oral glucose tolerance was significantly improved for both DJ and SG at four weeks after surgery (p < 0.05). At the 34th postoperative week, SG had significantly lower area under the curve during oral glucose tolerance test compared to sham (p = 0.007). SG had significantly lower HbA1c compared to sham at 12 weeks; (mean ± SEM) 4.3 ± 0.1 % versus 5.2 ± 0.3 % (p < 0.05) and compared to both DJ and sham 34 weeks after surgery [median (75 %;25 %)] 5.2 (6.0; 4.3) % versus 7.0 (7.5; 6.7) % and 7.3 (7.6; 6.7) % (p = 0.009). Serum gastrin levels were markedly elevated for SG compared to DJ and sham; 188.0 (318.0; 121.0) versus 77.5 (114.0; 58.0) and 68.0 (90.0; 59.5) pmol/L (p = 0.004) at six weeks and 192.0 (587.8; 110.8) versus 65.5 (77.0; 59.0) and 69.5 (113.0; 55.5) (p = 0.001) 36 weeks after surgery.

CONCLUSION

Sleeve gastrectomy induces hypergastrinemia, lowers HbA1c, and improves glycemic control in Goto-Kakizaki rats. Sleeve gastrectomy is superior to duodenojejunostomy as treatment of type 2 diabetes mellitus in this animal model.

Diabetes disease progression in Goto-Kakizaki rats: effects of salsalate treatment

This study investigates the antidiabetic effects of salsalate on disease progression of diabetes in non-obese diabetic Goto-Kakizaki (GK) rats, an experimental model of type 2 diabetes. Salsalate was formulated in rat chow (1,000 ppm) and used to feed rats from 5 to 21 weeks of age. At 5 weeks of age, GK and Wistar (WIS) control rats were subdivided into four groups, each composed of six rats: GK rats with standard diet (GK-C); GK rats with salsalate-containing diet (GK-S); WIS rats with standard diet (WIS-C); and WIS rats with salsalate-containing diet (WIS-S). The GK-C rats (167.2±11.6 mg/dL) showed higher blood glucose concentrations than WIS-C rats (133.7±4.9 mg/dL, P<0.001) at the beginning of the experiment, and had substantially elevated blood glucose from an age of 15 weeks until sacrifice at 21 weeks (341.0±133.6 mg/dL). The GK-S rats showed an almost flat profile of blood glucose from 4 weeks (165.1±11.0 mg/dL) until sacrifice at 21 weeks of age (203.7±22.2 mg/dL). While this difference in blood glucose between 4 and 21 weeks in GK-S animals was significant, blood glucose at 21 weeks was significantly lower in GK-S compared to GK-C animals. At sacrifice, salsalate decreased plasma insulin (GK-S =1.0±0.3; GK-C =2.0±0.3 ng/mL, P<0.001) and increased plasma adiponectin concentrations (GK-S =15.9±0.7; GK-C =9.7±2.0 μg/mL, P<0.001). Salsalate also lowered total cholesterol in GK-S rats (96.1±8.5 mg/dL) compared with GK-C rats (128.0±11.4 mg/dL, P<0.001). Inflammation-related genes (Ifit1 and Iigp1) exhibited much higher mRNA expression in GK-C rats than WIS-C rats in liver, adipose, and muscle tissues, while salsalate decreased the Ifit1 and Iigp1 mRNA only in adipose tissue. These results suggest that salsalate acts to both increase adiponectin and decrease adipose tissue-based inflammation while preventing type 2 diabetes disease progression in GK rats.

A review of rodent models of type 2 diabetic skeletal fragility

Evidence indicating that adult type 2 diabetes (T2D) is associated with increased fracture risk continues to mount. Unlike osteoporosis, diabetic fractures are associated with obesity and normal to high bone mineral density, two factors that are typically associated with reduced fracture risk. Animal models will likely play a critical role in efforts to identify the underlying mechanisms of skeletal fragility in T2D and to develop preventative treatments. In this review we critically examine the ability of current rodent models of T2D to mimic the skeletal characteristics of human T2D. We report that although there are numerous rodent models of T2D, few have undergone thorough assessments of bone metabolism and strength. Further, we find that many of the available rodent models of T2D have limitations for studies of skeletal fragility in T2D because the onset of diabetes is often prior to skeletal maturation and bone mass is low, in contrast to what is seen in adult humans. There is an urgent need to characterize the skeletal phenotype of existing models of T2D, and to develop new models that more closely mimic the skeletal effects seen in adult-onset T2D in humans.

Population pharmacodynamic modeling of exenatide after 2-week treatment in STZ/NA diabetic rats

The purpose of this study is to investigate the effect of exenatide on glycemic control following two administration routes in a streptozotocin/nicotinamide (STZ/NA)-induced diabetic rat model, and to develop a pharmacodynamic model to better understand the disease progression and the action of exenatide in this experimental system. Two groups of STZ/NA-induced diabetic rats were treated for 2 weeks with 20 (μg/kg/day) of exenatide, either by continuous subcutaneous (SC) infusion or two SC injections daily. Disease progression was associated with slower glucose utilization. Fasting blood glucose was significantly reduced by 30 mg/dL in both treatment groups at the end of 2 weeks. A subsequent intravenous glucose tolerance test (IVGTT) confirmed an improved glucose tolerance in both treatment groups; however, overall glycemic control was similar between groups, likely due to the relatively low and short-term drug exposure. A population indirect response model was successfully developed to simultaneously describe the STZ/NA-induced disease progression, responses to an IVGTT, and exenatide effects on these systemic challenges. The unified model includes a single set of parameters, and the cumulative area under the drug-receptor concentration curve was used as a unique driving force to account for systemic effects long after drug elimination.

Effects of high fat feeding on liver gene expression in diabetic goto-kakizaki rats

Effects of high fat diet (HFD) on obesity and, subsequently, on diabetes are highly variable and modulated by genetics in both humans and rodents. In this report, we characterized the response of Goto-Kakizaki (GK) rats, a spontaneous polygenic model for lean diabetes and healthy Wistar-Kyoto (WKY) controls, to high fat feeding from weaning to 20 weeks of age. Animals fed either normal diet or HFD were sacrificed at 4, 8, 12, 16 and 20 weeks of age and a wide array of physiological measurements were made along with gene expression profiling using Affymetrix gene array chips. Mining of the microarray data identified differentially regulated genes (involved in inflammation, metabolism, transcription regulation, and signaling) in diabetic animals, as well as the response of both strains to HFD. Functional annotation suggested that HFD increased inflammatory differences between the two strains. Chronic inflammation driven by heightened innate immune response was identified to be present in GK animals regardless of diet. In addition, compensatory mechanisms by which WKY animals on HFD resisted the development of diabetes were identified, thus illustrating the complexity of diabetes disease progression.

Exercise training prevents decrease in luminal capillary diameter of skeletal muscles in rats with type 2 diabetes

The purpose of this study was to examine whether exercise training can prevent microangiopathy of skeletal muscles in rats with type 2 diabetes and if succinate dehydrogenase (SDH) activity, an indicator of mitochondrial oxidative enzyme activity, is involved in the prevention of microangiopathy. Six-week-old male Goto-Kakizaki (GK) rats and age-matched male Wistar rats (control group (Con)) were used. GK rats were randomly assigned to nonexercise (DB) and exercise (DBEx) groups. The DBEx group was trained on a treadmill 5 times a week for 3 weeks. No significant differences in the capillary-to-fibre ratio or the capillary density were observed between the 3 groups. The luminal capillary diameter of the DB group was significantly lower than that of the Con group, whereas the capillary diameter of the DBEx group was significantly higher than that of the DB group. In addition, SDH activity was significantly higher in the DBEx group than in the Con and DB groups. Microangiopathy of skeletal muscles in type 2 diabetes was correlated with a decrease in the luminal capillary diameter, which was prevented by exercise training. Thus, the mitochondrial oxidative capacity appears to be involved in the overall mechanism by which exercise prevents microangiopathy.

Pharmacokinetics of salsalate and salicylic acid in normal and diabetic rats

The pharmacokinetics (PK) of salsalate (SS) and salicylic acid (SA) was assessed in normal Wistar and diabetic Goto-Kakizaki rats. Three PK studies were conducted: (1) PK of SA in normal rats after intravenous dosing of SA at 20, 40, 80 mg/kg. (2) PK of SS and SA in normal rats after oral dosing of SS at 28, 56, 112 mg/kg. (3) PK during 4 months feeding of SS-containing diet in both normal and diabetic rats. The disposition of SS and SA were evaluated simultaneously using a pharmacokinetic model comprising several transit absorption steps and linear and nonlinear dual elimination pathways for SA. The results indicated that the nonlinear elimination pathway of SA only accounted for a small fraction of the total clearance (< 12%) at therapeutic concentrations. A flat profile of SA was observed after oral dosing of SS, particularly at a high dose. The possible reasons for this flat profile were posed. During the SS-diet feeding, the diabetic rats achieved lower blood concentrations of SA than normal rats with a higher apparent clearance (CL/F), possibly due to incomplete (47%) bioavailability. Such CL/F decreased with age in both diabetic and normal rats. The effect of diabetes on SA pharmacokinetics may necessitate increased dosing in the future usage of SS in diabetes.

Pharmacokinetic/pharmacodynamic modeling in inflammation

Inflammation is an array of immune responses to infection and injury. It results from a complex immune cascade and is the basis of many chronic diseases such as arthritis, diabetes, and cancer. Numerous mathematical models have been developed to describe the disease progression and effects of anti-inflammatory drugs. This review illustrates the state of the art in modeling the effects of diverse drugs for treating inflammation, describes relevant biomarkers amenable to modeling, and summarizes major advantages and limitations of the published pharmacokinetic/ pharmacodynamic (PK/PD) models. Simple direct inhibitory models are often used to describe in vitro effects of anti-inflammatory drugs. Indirect response models are more mechanism based and have been widely applied to the turnover of symptoms and biomarkers. These, along with target-mediated and transduction models, have been successfully applied to capture the PK/PD of many anti-inflammatory drugs and describe disease progression of inflammation. Biologics have offered opportunities to address specific mechanisms of action, and evolve small systems models to quantitatively capture the underlying physiological processes. More advanced mechanistic models should allow evaluation of the roles of some key mediators in disease progression, assess drug interactions, and better translate drug properties from in vitro and animal data to patients.