Physiological changes induced by salt intake in female Spontaneously Diabetic Torii-Lepr(fa) (SDT fatty) rat, a novel obese type 2 diabetic model

Effects of excessive sodium chloride loading in the spontaneously diabetic torii (SDT) fatty rats, a preclinical model of type 2 diabetes mellitus

Type 2 diabetes mellitus represents an international health concern with its growing number of patients worldwide. At the same time, excessive salt consumption is also seen as a major cause of diseases such as hypertension and may expedite renal complications in diabetic patients. In this study, we investigated the effects of excessive sodium chloride supplementation on the kidney of the Spontaneously Diabetic Torii-Lepr^fa (SDT fatty) rat, an obese type 2 diabetes model. Male and female SDT fatty rats and normal Sprague-Dawley (SD) rats at 5 weeks of age were loaded with 0.3% sodium chloride (NaCl) in drinking water for 13 weeks. Blood serum and urinary parameters were observed throughout the experiment and kidney samples were examined in histopathological and genetical analyses. Significant changes on the body weight, blood pressure, urine volume, creatinine clearance, blood urea nitrogen (BUN), relative gene expressions of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), monocyte chemotactic protein-1 (MCP-1) and transforming growth factor-β (TGF-β) were observed in the salt-loaded male SDT fatty rats. Urinary L-type fatty acid-binding protein (L-FABP) and albumin levels were higher observed in the salt-loaded male SDT fatty rats throughout the period, but urinary albumin levels in the female SDT fatty rats remain unchanged. In the kidney, slight Armani-Ebstein changes, tubular degeneration, hyaline cast, and inflammatory cell infiltration were observed in female SDT fatty rats while the levels of some changes were higher in the salt-loaded group. The kidney of the salt-loaded male SDT fatty rats demonstrated a higher degree of lesions compared to the female group and the male unloaded group. Histopathological changes in salt-loaded SDT fatty rats show that excessive salt consumption may act as a diabetic pathology exacerbation factor, but the pathology may be influenced by gender difference. Urinary L-FABP levels may act as a useful biomarker to detect slight tubular damages in the kidney. Excessive salt loading was shown to exacerbate the renal injury in SDT fatty rats.

The Possibility of Urinary Liver-Type Fatty Acid-Binding Protein as a Biomarker of Renal Hypoxia in Spontaneously Diabetic Torii Fatty Rats

BACKGROUND

Renal hypoxia is an aggravating factor for tubulointerstitial damage, which is strongly associated with renal prognosis in diabetic kidney disease (DKD). Therefore, urinary markers that can detect renal hypoxia are useful for monitoring DKD.

OBJECTIVE

To determine the correlation between urinary liver-type fatty acid-binding protein (L-FABP) and renal hypoxia using a novel animal model of type 2 diabetes.

METHODS

Male spontaneously diabetic Torii (SDT) fatty rats (n = 6) were used as an animal model of type 2 diabetes. Age- and sex-matched Sprague-Dawley (SD) rats (n = 8) were used as controls. Body weight, systolic blood pressure, and blood glucose levels were measured at 8, 12, 16, and 24 weeks of age. Urine samples and serum and kidney tissues were collected at 24 weeks of age. Microvascular blood flow index (BFI) was measured using diffuse correlation spectroscopy before sampling both the serum and kidneys for the evaluation of renal microcirculation at the corticomedullary junction.

RESULTS

Obesity, hyperglycemia, and hypertension were observed in the SDT fatty rats. Focal glomerular sclerosis, moderate interstitial inflammation, and fibrosis were significantly more frequent in SDT fatty rats than in SD rats. While the frequency of peritubular endothelial cells and phosphoendothelial nitric oxide synthase levels were similar in both types of rats, the degree of renal hypoxia-inducible factor-1α (HIF-1α) expression was significantly higher (and with no change in renal vascular endothelial growth factor expression levels) in the SDT fatty rats. Urinary L-FABP levels were significantly higher and renal microvascular BFI was significantly lower in the SDT fatty rats than in the SD rats. Urinary L-FABP levels exhibited a significant positive correlation with renal HIF-1α expression and a significant negative correlation with renal microvascular BFI.

CONCLUSIONS

Urinary L-FABP levels reflect the degree of renal hypoxia in DKD in a type 2 diabetic animal model. Urinary L-FABP may thus prove useful as a renal hypoxia marker for monitoring DKD in patients with type 2 diabetes in clinical practice.

High-Salt Intake Ameliorates Hyperglycemia and Insulin Resistance in WBN/Kob-Leprfa/fa Rats: A New Model of Type 2 Diabetes Mellitus

High-salt intake is a major risk factor for developing hypertension in type 2 diabetes mellitus, but its effects on glucose homeostasis are controversial. We previously found that high-salt intake induces severe hypertension in WBN/Kob diabetic fatty (WBKDF) rats. In the present study, we examined the effects of a high-salt intake on glucose homeostasis in WBKDF rats. Male WBKDF rats and age-matched Wistar rats at 6 weeks of age were each divided into two groups and fed either a normal-sodium (NS, 0.26%) diet or high-sodium (HS, 8%) diet for 7 weeks. Systolic blood pressure and urine volume were increased in WBKDF-HS and Wistar-HS. Body weight gain and food consumption were comparable between NS and HS in both strains. Plasma and urine glucose levels were significantly increased in WBKDF-NS but not in WBKDF-HS. HOMA-IR in WBKDF-HS was significantly lower compared with that in WBKDF-NS. The high plasma adiponectin level in WBKDF-NS compared with that in Wistar-NS was further enhanced in WBKDF-HS. Glycogen deposits and fat droplets in the livers of WBKDF-HS were reduced compared with those of WBKDF-NS. The present study demonstrated that HS intake ameliorated hyperglycemia and insulin resistance in WBKDF rats, which may be due to increased plasma levels of adiponectin.

Effects of high-sodium intake on systemic blood pressure and vascular responses in spontaneously diabetic WBN/Kob-Leprfa/fa rats

The prevalence of type 2 diabetes mellitus (T2DM) and hypertension has markedly increased worldwide. The purpose of the present study was to examine the effects of a high‐salt intake on the systolic blood pressure (SBP) and vascular responses in WBN/Kob‐Lepr^fa/fa (WBKDF) rats, a new spontaneous animal model of T2DM. Male WBKDF rats and age‐matched Wistar rats at 6 weeks of age were each divided into two groups and fed either a normal‐sodium (NS, 0.26%) diet or high‐sodium (HS, 8%) diet for 14 weeks: (i) Wistar rats on NS diet (Wistar‐NS); (ii) Wistar rats on HS diet (Wistar‐HS); (iii) WBKDF rats on NS diet (WBKDF‐NS); (iv) WBKDF rats on HS diets (WBKDF‐HS). Neither WBKDF‐NS nor Wistar‐NS rats showed significant changes in SBP throughout the experiment, but both WBKDF‐HS and Wistar‐HS exhibited significant elevation of SBP, which was more prominent (P<.01) in WBKDF‐HS than in Wistar‐HS. Phenylephrine‐induced contractions of isolated thoracic aortic rings were significantly (P<.01) enhanced in WBKDF‐HS and Wistar‐HS compared with the respective strain of rats on the NS diet. In contrast, acetylcholine‐ and nitroprusside‐induced relaxation were significantly (P<.01) diminished in both WBKDF‐HS and Wistar‐HS, and these HS diet‐induced changes were more profound (P<.01) in WBKDF rats than in Wistar rats. Significantly (P<.05) higher plasma concentrations of 8‐iso‐prostaglandin F_2α and sodium ions were observed in WBKDF‐HS than in Wistar‐HS. The current study demonstrated that WBKDF‐HS rats developed salt‐sensitive hypertension associated with vascular dysfunction. The WBKDF rat may be a useful model for investigating the etiology of hypertension with T2DM.

Monosodium Glutamate Dietary Consumption Decreases Pancreatic β-Cell Mass in Adult Wistar Rats

Background

The amount of dietary monosodium glutamate (MSG) is increasing worldwide, in parallel with the epidemics of metabolic syndrome. Parenteral administration of MSG to rodents induces obesity, hyperglycemia, hyperlipidemia, insulin resistance, and type 2 diabetes. However, the impact of dietary MSG is still being debated. We investigated the morphological and functional effects of prolonged MSG consumption on rat glucose metabolism and on pancreatic islet histology.

Methods

Eighty adult male Wistar rats were randomly subdivided into 4 groups, and test rats in each group were supplemented with MSG for a different duration (1, 3, 6, or 9 months, n=20 for each group). All rats were fed ad libitum with a standard rat chow and water. Ten test rats in each group were provided MSG 2 mg/g body weight/day in drinking water and the 10 remaining rats in each group served as non-MSG treated controls. Oral glucose tolerance tests (OGTT) were performed and serum insulin measured at 9 months. Animals were sacrificed at 1, 3, 6, or 9 months to examine the histopathology of pancreatic islets.

Results

MSG-treated rats had significantly lower pancreatic β-cell mass at 1, 6 and 9 months of study. Islet hemorrhages increased with age in all groups and fibrosis was significantly more frequent in MSG-treated rats at 1 and 3 months. Serum insulin levels and glucose tolerance in MSG-treated and untreated rats were similar at all time points we investigated.

Conclusion

Daily MSG dietary consumption was associated with reduced pancreatic β-cell mass and enhanced hemorrhages and fibrosis, but did not affect glucose homeostasis. We speculate that high dietary MSG intake may exert a negative effect on the pancreas and such effect might become functionally significant in the presence or susceptibility to diabetes or NaCl; future experiments will take these crucial cofactors into account.

Upregulation of caveolin-1 contributes to aggravated high-salt diet-induced endothelial dysfunction and hypertension in type 1 diabetic rats

AIMS

Endothelial dysfunction and hypertension is more common in individuals with diabetes than in the general population. This study was aimed to investigate the underlying mechanisms responsible for endothelial dysfunction of type 1 diabetic rats fed with high-salt diet.

MAIN METHODS

Type 1 diabetes (DM) was induced by intraperitoneal injection of streptozotocin (70 mg·kg(-1)). Normal or diabetic rats were randomly fed high-salt food (HS, 8% NaCl) or standard food (CON) for 6 weeks.

KEY FINDINGS

Both HS (143±10 mmHg) and DM+HS (169±11 mmHg) groups displayed significantly higher systolic blood pressure than those in the CON group (112±12 mmHg, P<0.01). DM+HS rats exhibited more pronounced impairment of vasorelaxation to acetylcholine and insulin compared with either DM or HS. Akt/endothelial nitric oxide synthase (eNOS) phosphorylation levels and nitric oxide (NO) concentration in DM+HS were significantly lower than in DM. The levels of caveolin-1 (cav-1) in DM+HS were significantly higher than that in DM and HS. Co-immunoprecipitation results showed increased interaction between cav-1 and eNOS in the DM+HS group. In the presence of cav-1 small interfering RNA (siRNA), eNOS phosphorylations in human umbilical vein endothelial cells (HUVEC) were significantly increased compared with control siRNA. Cav-1 was slightly but not significantly lower in HUVEC cultured with high glucose and high-salt buffer solution and pretreated with wortmannin or l-nitro-arginine methyl ester.

SIGNIFICANCE

Impaired endothelial Akt activation and increased cav-1 expression and resultant decreased eNOS activation contributes to aggravated high-salt diet-induced endothelial dysfunction and hypertension in DM rats.