The intracellular mechanism of insulin resistance in the hamster pancreatic ductal adenocarcinoma model

Obesity and pancreatic cancer

BACKGROUND

Pancreatic cancer is an invariably fatal malignancy. Cigarette smoking and diabetes are established risk factors, but over the last two decades studies have shown that excess adiposity is an additional independent risk factor with 30-50% of cases thought to be attributed to nutritional factors. The aim of this narrative review is to analyze all the epidemiological evidence on the topic and possible pathophysiology.

METHODS

We searched PubMed, Embase, Cochrane Library and Medline, and all available evidence was included. We firstly analyze meta- and pooled analysis. Then we discuss individual studies to identify sources of discrepancies between studies and attempt to delineate pathophysiology.

RESULTS

It is estimated that obese individuals have a relative risk (RR) ranging between 1.19 and 1.47, when compared with those of normal weight, regardless of diabetes or smoking status. No significant differences were found between gender.

CONCLUSION

There is a measurable increased risk of developing pancreatic cancer in obese individuals, and excess adiposity is related to the condition with a "dose-response" curve. Hyperinsulinemia and possibly hyperestrogenism secondary to a metabolic syndrome, and independently from diabetes status, appear to be the key elements of the pathogenesis in pancreatic cancer secondary to excess body fat. Increased efforts should therefore be made in tackling the epidemic levels of obesity in the Western world countries.

Early diagnosis of pancreatic adenocarcinoma: role of stroma, surface proteases, and glucose-homeostatic agents

OBJECTIVES

New-onset diabetes in pancreatic adenocarcinoma is due to a combination of insulin resistance and decreased β-cell function. Its differentiation from the common type 2 diabetes is the prerequisite for early diagnosis of pancreatic adenocarcinoma. Little attention has been paid to pancreatic stroma and surface proteases.

METHODS

The activated fibroblasts selectively express fibroblast activation protein α, a structural homolog of the ubiquitously expressed dipeptidyl peptidase 4. Their role in pancreatic carcinogenesis is reviewed.

RESULTS

Homodimers and heterodimers of both enzymes display high specificity for peptides and proteins with penultimate proline or alanine. Most glucose-homeostatic agents are candidate substrates of these enzymes. The biological activity of truncated substrates is decreased or absent.

CONCLUSIONS

The interactions of surface proteases with glucose-homeostatic agents may adequately explain the evolution of diabetes associated with pancreatic adenocarcinoma and differentiate it from the common type 2 diabetes.

Promoting Effects of Sucrose-rich Diet on N-Nitrosobis (2-oxopropyl) amine-induced Pancreatic Carcinogenesis in Hamsters

It has been reported that there is an association between pancreatic cancer and obesity, impaired glucose metabolism and diabetes based on excess dietary fat and sugar intakes. A number of studies have suggested that a high-fat diet increases development of carcinomas in various organs and possible risk factors for pancreatic cancer. However, how an excess sugar intake promotes pancreatic carcinogenesis is still unknown. In the present study, we investigated the influence of an excess sugar intake on pancreatic carcinogenesis by administration of a sucrose-rich diet in which starch was replaced by sucrose in order to contain the same calories and other nutrients. Two similar experiments were performed. Six-week-old male Syrian golden hamsters were given N-nitrosobis (2-oxopropyl) amine (BOP) at a dose of 50 and 20 mg/kg body weight as a carcinogen in Week 0 and 1, respectively. In Week 2, the animals were divided into control and experimental groups. In experiment 1, 15 animals received a control diet or sucrose-rich diet in which 100% of the starch was replaced by sucrose, respectively. Since five animals fed on the sucrose-rich diet died by Week 12, the diet was changed to a sucrose-rich diet in which 50% of the starch was replaced by sucrose. In experiment 2, 15 animals received a control diet or sucrose-rich diet in which 50 or 20% of the starch was replaced by sucrose, respectively. All animals were sacrificed 25 weeks after the start of the experiment, and histological examination of the pancreas was performed. No significant difference was seen in the body weight at the end of the experiment. There were no significant differences in the glycosylated hemoglobin (HbA1c) and serum triglyceride, total cholesterol and HDL-cholesterol levels between the control and sucrose-rich diet groups in experiments 1 and 2. The incidence and number of carcinomas increased in hamsters fed the sucrose-rich diet compared with the control diet in experiments 1 and 2. These results suggest that an excess sucrose intake may promote the development of pancreatic cancer in hamsters.

Diabetes mellitus: a risk factor for pancreatic cancer?

The relationship between pancreatic cancer (PC) and diabetes is controversial. While some investigators assume that type II diabetes is a predisposition to PC, recent data argue that diabetes and altered glucose metabolism are a consequence of PC, and yet, the clinical presentation of the altered glucose metabolism in these patients varies considerably. Around 70% of patients with PC have impaired glucose tolerance (IGT) or frank diabetes. Of these, nearly 60% show an improvement of IGT or diabetes after surgery, whereas the rest show only mild or no improvement. It appears that biologically there are three types of PC: (1) PC not associated with IGT or diabetes; (2) PC associated with IGT or diabetes in which the abnormality improves postoperatively; (3) PC associated with IGT or diabetes in which the abnormality does not improve postoperatively. Based on our own studies, we suggest that the reason for impaired glucose metabolism in most patients is the alteration of islet cells either by the carcinogen directly, or by diabetogenic substances released by cancer cells. The extent of the islet alteration (i.e. focal or diffuse) may determine whether the removal of tumor alone can improve the metabolic alteration. The elucidation of the mechanism is of immense importance for providing an early tumor marker and for developing preventative or therapeutic modalities.

Potential involvement of the cyclooxygenase-2 pathway in the regulation of tumor-associated angiogenesis and growth in pancreatic cancer

Background

Gleevec (aka STI571, Imatinib) is a recently FDA approved anti-tumor drug for chronic myelogenous leukemia. Gleevec binds specifically to BCR-ABL tyrosine kinase and inhibit the tyrosine kinase activity. It cross-reacts with another two important membrane tyrosine kinase receptors, c-kit and PDGF receptors. We sought to investigate if Gleevec has a potential role in treatment of non-small cell lung cancer.

Results

We have shown that Gleevec alone can inhibit the A549 lung cancer cell growth in dose-dependent manner, and the optimal concentration of Gleevec inhibition of A549 cell growth is at the range of 2–3 μM (IC50). We have also shown that A549 cells are resistant to cisplatin treatment (IC50 64 μM). Addition of Gleevec to the A549 cells treated with cisplatin resulted in a synergistic cell killing effect, suggesting that Gleevec can potentiate the effect of cisplatin on A549 cells. We also showed that the A549 lung cancer cells expresses the platelet derived growth factor receptor α, and the inhibitory effects of Gleevec on A549 cells is likely mediated through inhibition of PDGFR α phosphorylation. We further tested 33 lung cancer patients' tumor specimens to see the frequency of PDGFR-α expression by tissue micro-arrays and immunohistochemistry. We found that 16 of the 18 squamous carcinomas (89%), 11 of the 11 adenocarcinomas (100%), and 4 of the 4 small cell lung cancers (100%) expressed PDGFR-α.

Conclusion

These results suggest a potential role of Gleevec as adjuvant therapeutic agent for treatment of non-small cell lung cancer.

The relationship between diabetes and pancreatic cancer

About 80% of pancreatic cancer patients have glucose intolerance or frank diabetes. This observation has led to the following two hypotheses: i. pancreatic cancer causes the associated diabetes and ii. the conditions associated with diabetes promote the development of pancreatic cancer. Evidence supporting both hypotheses has been accumulated in previous studies. This article reviews these studies, especially those that have been conducted recently.

High prevalence of diabetes in patients with pancreatic cancer in central Anatolia, Turkey

Tumor-induced pancreatic damage or insulin resistance may be responsible for diabetes in pancreatic cancer (PC) patients, but the exact cause of association remains controversial. In this study, we aimed to investigate the prevalence of diabetes in patients with PC in central Anatolia, Turkey, and to evaluate whether diabetes is caused by PC. A total of 40 patients with primary PC were enrolled in the study. 13 (32.5%) of the patients had diabetes before PC diagnosis. Oral glucose tolerance test was performed in the remaining 27 patients. The period between the diagnosis of diabetes and detection of PC was less than 1 year in seven (17.5%) patients who had previous diabetes. Recent-onset diabetes and impaired glucose tolerance were detected in 13 (32.5%) and two (5%) of the PC patients, respectively. The prevalence of recent-onset and shortly-before-diagnosed diabetes has been found very high (50%) in our patients with PC. Interestingly, we determined higher levels of insulin and C-peptide in PC patients having abnormal glucose tolerance than patients having normal glucose tolerance. In conclusion, as it has been reported in other population, we determined high prevalence of diabetes in PC patients in central Anatolia. High insulin and C-peptide level indicate that different mechanisms such as insulin resistance may be responsible for abnormal glucose tolerance in PC patients other than the tumor caused insulin deficiency.

5-Lipoxygenase and leukotriene B(4) receptor are expressed in human pancreatic cancers but not in pancreatic ducts in normal tissue

The 5-lipoxygenase (5-LOX) pathway is critical for pancreatic cancer cell growth and escape from apoptosis. Inhibition of 5-LOX blocks proliferation and induces apoptosis in human pancreatic cancer cells. However, the expression of 5-LOX and its downstream signaling pathway have not been investigated in human pancreatic adenocarcinoma. Reverse transcriptase-polymerase chain reaction revealed expression of 5-LOX mRNA in all pancreatic cancer cell lines tested including, PANC-1, AsPC-1, and MiaPaCa2 cells, but not in normal pancreatic ductal cells. The expression of 5-LOX protein in pancreatic cancer cell lines was demonstrated by Western blotting. Finally, 5-LOX up-regulation in human pancreatic cancer tissues was verified by intense positive staining in cancer cells by immunohistochemistry. Staining for the 5-LOX protein was particularly evident in the ductal components of the more differentiated tumors but not in ductal cells in normal pancreatic tissues from cadaver donors. Immunohistochemistry also revealed strong staining of cancer tissues with an antibody to the receptor of the downstream 5-LOX metabolite, leukotriene B(4). The current study demonstrated marked expression of 5-LOX and the leukotriene B(4) receptor in human pancreatic cancer tissues. These findings provide further evidence of up-regulation of this pathway in pancreatic cancer and that LOX inhibitors are likely to be valuable in the treatment of this dreadful disease.

Physical activity, anthropometric factors and risk of pancreatic cancer: results from the Canadian enhanced cancer surveillance system

To explore the hypothesis that insulin resistance may be an etiologic factor in pancreatic cancer, we assessed the pancreatic cancer risk associated with anthropometric factors and physical activity, both of which are important determinants of insulin sensitivity in humans. Three hundred and twelve patients with histologically confirmed pancreatic cancer were compared to 2,919 controls in a population-based, case-control study in 7 of the 10 Canadian provinces. Participants were asked to report their exposure status for the period 2 years before interview. Men in the highest quartile of body mass index (BMI, > or =28.3 kg/m(2)) were at increased risk of pancreatic cancer [adjusted odds ratio (OR) = 1.90, 95% confidence interval (CI) 1.08-3.35]. In addition, men who reported a decrease in weight of at least 2.9% from their lifetime maximum were at reduced risk compared to those reporting a < or =2.9% loss (> or =10.2% loss, OR = 0.51, 95% CI 0.30-0.86). BMI 2 years before interview was not associated with pancreatic cancer risk among women, though those reporting a > or =12.5% decrease in weight from their lifetime maximum had substantially lower risk compared to those in the baseline quartile (OR = 0.53, 95% CI 0.29-0.99). After adjustment for age, province of residence, dietary intake and anthropometric factors, men in the highest quartile of the composite moderate and strenuous physical activity index were at reduced risk of pancreatic cancer (OR = 0.53, 95% CI 0.31-0.90). Physical activity did not appear to be associated with pancreatic cancer among women, though a tendency for reduced risk with increasing levels of strenuous activity was suggested (p for trend = 0.06). Our findings support the hypothesis that insulin resistance is an etiologic factor in the development of pancreatic neoplasms among men and possibly women.

Differentiation of islet cells in long-term culture

Our previous studies in the hamster pancreatic cancer model have shown that exocrine pancreatic cancer arises from ductal/ductular cells, as well as from within the islets, most probably from islet precursor (stem) cells. To identify and characterize these cells, we established a long-term culture from isolated hamster islets and investigated their growth, differentiation, and expression of biomarkers. Islets maintained their original form and structure within the first 14 days in culture. However, beginning at day 7, ductular structures began to form within the islets. At day 21 in culture, acinar cells, intermediary cells, oncocytes, and cells comparable to pancreatic hepatocytes also appeared between ductular and endocrine cells. The number of duct-like cells gradually increased, whereas the number of hormone-producing cells decreased. After 35 days in culture, the exocrine cells disappeared, and undifferentiated cells formed a monolayer. These cells expressed cytokeratins, alpha1-antitrypsin, transforming growth factor-alpha, epidermal growth factor receptor, carbonic anhydrase II, vimentin, laminin, and showed binding to tomato lectin and Phaseolus vulgaris leukoagglutinin. They did not express the regulatory transcriptional factors, insulin-promoting factor 1, NKx6.1, Pax6, and NeuroD. The results thus indicate that islet cells have potential to form exocrine cells. At present, it is not clear whether these cells originate from preexisting stem cells or from transdifferentiated islet cells.