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Excessive islet NO generation in type 2 diabetic GK rats coincides with abnormal hormone secretion and is counteracted by GLP-1.

Salehi A, Meidute Abaraviciene S, Jimenez-Feltstrom J, Ostenson CG, Efendic S, Lundquist I - PLoS ONE (2008)

Bottom Line: Pharmacological blockade of islet NO production by the NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) greatly improved hormone secretion from GK islets suggesting islet NOS activity being an important target to inactivate for amelioration of islet cell function.The incretin hormone GLP-1, which is used in clinical practice suppressed iNOS and ncNOS expression and activity with almost full restoration of insulin release and partial restoration of glucagon release.The results suggest that abnormally increased NO production within islet cells is a significant player in the pathogenesis of type 2 diabetes being counteracted by GLP-1 through PKA-dependent, nonproteasomal mechanisms.

View Article: PubMed Central - PubMed

Affiliation: Department of Clinical Science, Universitetssjukhuset Malmö Allmäna Sjukhus, Division of Endocrine Pharmacology, Karolinska Institute, Stockholm, Sweden. S_Albert.Salehi@med.lu.se

ABSTRACT

Background: A distinctive feature of type 2 diabetes is inability of insulin-secreting beta-cells to properly respond to elevated glucose eventually leading to beta-cell failure. We have hypothesized that an abnormally increased NO production in the pancreatic islets might be an important factor in the pathogenesis of beta-cell dysfunction.

Principal findings: We show now that islets of type 2 spontaneous diabetes in GK rats display excessive NO generation associated with abnormal iNOS expression in insulin and glucagon cells, increased ncNOS activity, impaired glucose-stimulated insulin release, glucagon hypersecretion, and impaired glucose-induced glucagon suppression. Pharmacological blockade of islet NO production by the NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) greatly improved hormone secretion from GK islets suggesting islet NOS activity being an important target to inactivate for amelioration of islet cell function. The incretin hormone GLP-1, which is used in clinical practice suppressed iNOS and ncNOS expression and activity with almost full restoration of insulin release and partial restoration of glucagon release. GLP-1 suppression of iNOS expression was reversed by PKA inhibition but unaffected by the proteasome inhibitor MG132. Injection of glucose plus GLP-1 in the diabetic rats showed that GLP-1 amplified the insulin response but induced a transient increase and then a poor depression of glucagon.

Conclusion: The results suggest that abnormally increased NO production within islet cells is a significant player in the pathogenesis of type 2 diabetes being counteracted by GLP-1 through PKA-dependent, nonproteasomal mechanisms.

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(a) NOS activities and hormone secretion in islets incubated at high glucose. Islet NO-production from ncNOS, iNOS and total NOS as well as insulin and glucagon release from islets of Wistar or GK rats incubated at 16.7 mmol/l glucose in the absence (open bars) and presence (dark bars) of 100 nmol/l GLP-1. Values are mean±s.e.m for 6–10 batches of islets at each point. *P<0.05; ** P<0.01; *** P<0.001. (b) Representative examples of Western blots of iNOS and ncNOS protein in the absence and presence of GLP-1 are shown.
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pone-0002165-g004: (a) NOS activities and hormone secretion in islets incubated at high glucose. Islet NO-production from ncNOS, iNOS and total NOS as well as insulin and glucagon release from islets of Wistar or GK rats incubated at 16.7 mmol/l glucose in the absence (open bars) and presence (dark bars) of 100 nmol/l GLP-1. Values are mean±s.e.m for 6–10 batches of islets at each point. *P<0.05; ** P<0.01; *** P<0.001. (b) Representative examples of Western blots of iNOS and ncNOS protein in the absence and presence of GLP-1 are shown.

Mentions: Fig. 4a, b and Table 2b shows the effect of GLP-1 on NOS activities and protein expression in islets incubated at high glucose (16.7 mmol/l). Again, NOS activities were increased in GK compared with Wistar islets. This was mainly due to increased iNOS activity (Fig. 4a). However, upregulation of NOS activities was not so pronounced in GK islets at high glucose as at low glucose possibly because NOS activities were already upregulated in vivo and in comparison high glucose increased NOS activities also in Wistar islets (Fig. 4a, b). NO production and Western blots show that GLP-1 reduced both expression and activities of iNOS and ncNOS (Fig. 4a, b, Table 2b). This suppression was associated with a prominent increase in glucose-stimulated insulin release and thus the impairment of glucose-induced insulin response in GK islets was efficiently counteracted (Fig. 4a). Moreover, while high glucose suppressed glucagon secretion in Wistar islets, negligible suppression by glucose was found in glucagon hypersecreting GK islets (compare Fig. 2a and 4a). GLP-1 reduced glucagon secretion in both types of islets (Fig. 2a). However, compared to Wistar, GK islets still displayed elevated glucagon secretion even after combination of high glucose and GLP-1 (Fig. 4a). The densitometric analysis showed that GLP-1 induced a marked suppression of both ncNOS and iNOS expression in GK as well as Wistar islets (Table 2b).


Excessive islet NO generation in type 2 diabetic GK rats coincides with abnormal hormone secretion and is counteracted by GLP-1.

Salehi A, Meidute Abaraviciene S, Jimenez-Feltstrom J, Ostenson CG, Efendic S, Lundquist I - PLoS ONE (2008)

(a) NOS activities and hormone secretion in islets incubated at high glucose. Islet NO-production from ncNOS, iNOS and total NOS as well as insulin and glucagon release from islets of Wistar or GK rats incubated at 16.7 mmol/l glucose in the absence (open bars) and presence (dark bars) of 100 nmol/l GLP-1. Values are mean±s.e.m for 6–10 batches of islets at each point. *P<0.05; ** P<0.01; *** P<0.001. (b) Representative examples of Western blots of iNOS and ncNOS protein in the absence and presence of GLP-1 are shown.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2367446&req=5

pone-0002165-g004: (a) NOS activities and hormone secretion in islets incubated at high glucose. Islet NO-production from ncNOS, iNOS and total NOS as well as insulin and glucagon release from islets of Wistar or GK rats incubated at 16.7 mmol/l glucose in the absence (open bars) and presence (dark bars) of 100 nmol/l GLP-1. Values are mean±s.e.m for 6–10 batches of islets at each point. *P<0.05; ** P<0.01; *** P<0.001. (b) Representative examples of Western blots of iNOS and ncNOS protein in the absence and presence of GLP-1 are shown.
Mentions: Fig. 4a, b and Table 2b shows the effect of GLP-1 on NOS activities and protein expression in islets incubated at high glucose (16.7 mmol/l). Again, NOS activities were increased in GK compared with Wistar islets. This was mainly due to increased iNOS activity (Fig. 4a). However, upregulation of NOS activities was not so pronounced in GK islets at high glucose as at low glucose possibly because NOS activities were already upregulated in vivo and in comparison high glucose increased NOS activities also in Wistar islets (Fig. 4a, b). NO production and Western blots show that GLP-1 reduced both expression and activities of iNOS and ncNOS (Fig. 4a, b, Table 2b). This suppression was associated with a prominent increase in glucose-stimulated insulin release and thus the impairment of glucose-induced insulin response in GK islets was efficiently counteracted (Fig. 4a). Moreover, while high glucose suppressed glucagon secretion in Wistar islets, negligible suppression by glucose was found in glucagon hypersecreting GK islets (compare Fig. 2a and 4a). GLP-1 reduced glucagon secretion in both types of islets (Fig. 2a). However, compared to Wistar, GK islets still displayed elevated glucagon secretion even after combination of high glucose and GLP-1 (Fig. 4a). The densitometric analysis showed that GLP-1 induced a marked suppression of both ncNOS and iNOS expression in GK as well as Wistar islets (Table 2b).

Bottom Line: Pharmacological blockade of islet NO production by the NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) greatly improved hormone secretion from GK islets suggesting islet NOS activity being an important target to inactivate for amelioration of islet cell function.The incretin hormone GLP-1, which is used in clinical practice suppressed iNOS and ncNOS expression and activity with almost full restoration of insulin release and partial restoration of glucagon release.The results suggest that abnormally increased NO production within islet cells is a significant player in the pathogenesis of type 2 diabetes being counteracted by GLP-1 through PKA-dependent, nonproteasomal mechanisms.

View Article: PubMed Central - PubMed

Affiliation: Department of Clinical Science, Universitetssjukhuset Malmö Allmäna Sjukhus, Division of Endocrine Pharmacology, Karolinska Institute, Stockholm, Sweden. S_Albert.Salehi@med.lu.se

ABSTRACT

Background: A distinctive feature of type 2 diabetes is inability of insulin-secreting beta-cells to properly respond to elevated glucose eventually leading to beta-cell failure. We have hypothesized that an abnormally increased NO production in the pancreatic islets might be an important factor in the pathogenesis of beta-cell dysfunction.

Principal findings: We show now that islets of type 2 spontaneous diabetes in GK rats display excessive NO generation associated with abnormal iNOS expression in insulin and glucagon cells, increased ncNOS activity, impaired glucose-stimulated insulin release, glucagon hypersecretion, and impaired glucose-induced glucagon suppression. Pharmacological blockade of islet NO production by the NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) greatly improved hormone secretion from GK islets suggesting islet NOS activity being an important target to inactivate for amelioration of islet cell function. The incretin hormone GLP-1, which is used in clinical practice suppressed iNOS and ncNOS expression and activity with almost full restoration of insulin release and partial restoration of glucagon release. GLP-1 suppression of iNOS expression was reversed by PKA inhibition but unaffected by the proteasome inhibitor MG132. Injection of glucose plus GLP-1 in the diabetic rats showed that GLP-1 amplified the insulin response but induced a transient increase and then a poor depression of glucagon.

Conclusion: The results suggest that abnormally increased NO production within islet cells is a significant player in the pathogenesis of type 2 diabetes being counteracted by GLP-1 through PKA-dependent, nonproteasomal mechanisms.

Show MeSH
Related in: MedlinePlus