Progression of Pancreatitis Prior to Diabetes Onset in WBN/Kob-Leprfa Rats

Abstract

ABSTRACT. We established the WBN/Kob-Lepr fa rat as a new congenic strain for the fa allele of the leptin receptor gene (Lepr). Homozygous (fa/fa) WBN/Kob-Lepr fa rats provide a model of non-insulin-dependent diabetes, although its onset is secondary to pancreatitis. In the present study, we compared histopathological observations of pancreatitis in each genotype of this rat, to examine its suitability as a model of pancreatitis. The histopathological findings of the pancreatitis revealed intense changes dependent on age, such as hemorrhage or hemosiderin deposition. The pancreatitis in homozygous (fa/fa) WBN/Kob-Lepr fa rats were more severe than those of WBN/ Kob rats. Pancreatitis is a common disorder of the exocrine the pancreas in dogs and cats. Clinical diagnosis of chronic pancreatitis is challenging because the disease is usually mild or subclinical, and its clinical signs are often the same as those of complicating or concurrent diseases. Pancreatitis is inflammation of the pancreas introduced by autodigestion and results in leakage of digestive enzymes. In rats and mice, experimental pancreatitis can be induced by ethanol feeding, [30] Original WBN/Kob rats were the spontaneous model of the pancreatitis [22]. Male WBN/Kob rats commonly develop chronic pancreatitis by the age of 3 months, while diabetes mellitus occurs at 9 months [10,18,19,28]. In contrast to males, female rats of this strain do not show pancreatitis.The leptin receptor fatty gene (Lepr fa ) is a recessive mutation that leads to leptin receptor deficiency, and homozygous animals (fa/fa) show obesity, hyperphagia, insulin resistance, hyperinsulinemia, and glucose intolerance [5,13,27,31]. The leptin receptor fatty gene accelerates pancreatitis and diabetes in WBN/Kob-Lepr fa rats. In the present study, we compared histopathological observations of pancreatitis in each genotype, to examine the suitability of using WBN/Kob-Lepr fa rats as a model of pancreatitis. Each genotype (fa/fa, +/fa, and +/+) of WBN/Kob-Lepr fa rats was produced by mating heterozygous (+/fa) males with heterozygous (+/fa) females. Genotyping of the fa mutation was performed according to the method described by Masuyama [15]. The animals were given a commercial diet (MF, Oriental Yeast Co. Tokyo, Japan) and tap water ad libitum, and were housed in an air-conditioned room (24  2C, 50~60% relative humidity, and lights on for 14 hr per day from 6:00 to 20:00). The number of animals in each group is detailed in Table 1. At 7, 9, 11, and 13 weeks of age, a blood sample was collected for each genotype (fa/fa, +/fa, and +/+), while blood glucose levels were measured with a portable glucose meter (Asensia Breeze) (Bayer-Sankyo). Rats were then sacrificed by ether anesthesia. The pancreas was removed, fixed overnight in Bouin's solution, and embedded in paraffin for histopathological analyses. Serial 4-m sections were cut and then stained with hematoxylin-eosin for histological examination. All sections were examined histopathologically and findings were graded from norm...

Role of Insulin Resistance in the Pathogenesis and Development of Type 2 Diabetes in WBN/Kob-<i>Lepr^fa</i> Rats

“…The high early insulin levels might represent compensation for high insulin resistance with hyperglycemia resulting when plasma insulin levels eventually drop. It was previously reported that impaired pancreatic β cells precede the onset of hyperglycemia [1, 2]. Insulin secretary capacity, as measured by the IVGTT, was enhanced by TGZ in our prophylactic study; however, plasma insulin levels in TGZ-treated rats at 8 and 9 weeks of age, when plasma insulin levels were sharply decreasing, were lower than those seen in the control rats.…”

Syphacia muris infection delays the onset of hyperglycemia in WBN/Kob-Lepr fa rats, a new type 2 diabetes mellitus model

“…These results are consistent with the fact that infection with pinworms is generally asymptomatic (Taffs, 1976). Since fa/fa rats develop pancreatitis with inflammatory infiltration prior to the onset of hyperglycemia (Akimoto et al, 2012), inflammatory cytokine production may trigger the onset of hyperglycemia in this model. Histopathological and immunohistochemical evaluations of the pancreas in the present study suggested that traces of inflammation, where exocrine components of the pancreas were not seen, were observed both in the S. muris-infected and the non-infected fa/fa rats.…”

High IL-1α production was induced in the WBN/Kob-Leprfa type 2 diabetes mellitus rat model and inhibited by Syphacia muris infection

“…In this study, we observed increased plasma levels of cytokines/chemokines in fa/fa rats with diabetes relative to those in age-matched control rats (Fig.1B). Likely, this increase in circulating cytokines results from pancreatic inflammation, as this strain naturally exhibits pancreatitis at 7 – 9 weeks of age (Akimoto et al, 2012). We detected high plasma levels of IL-1α rather than IL-1β which is known to associate with T2DM (Fig.1B and Fig.…”

“…The WBN/Kob- Lepr fa ( fa/fa ) rat is a new congenic strain established by introducing the leptin receptor fatty gene ( Lpr fa ), a spontaneous mutation derived from Zucker-fatty rats that develop obesity and hyperinsulinemia consequent to leptin receptor dysfunction (Zucker, 1965; Chua et al, 1996), into the parental WBN/Kob rat genome (Akimoto et al, 2008). Previous reports revealed that fa/fa rats develop hyperglycemia at 9 weeks of age, evidenced by impaired glucose tolerance, insulin resistance, and dyslipidemia in a manner similar to human T2DM8 (Akimoto et al, 2008; Akimoto et al, 2012; Kaji et al, 2012; Okuno et al, 2013; Nagakubo et al, 2014), thus suggesting that the fa/fa rat is useful as a new model of T2DM.…”