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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 Confocal microscopy of islets directly isolated ex vivo from the GK rat. The islets were double-immunolabelled for insulin or glucagon and iNOS and analysed by confocal microscopy. Insulin staining and iNOS staining appear, respectively, as red (A) and green (B) fluorescence. Co-localization of insulin/iNOS is seen as orange-yellowish fluorescence (C). Similarly glucagon staining and iNOS staining appear, respectively, as red (D) and green (E) fluorescence. Co-localization of glucagon/iNOS is seen as orange-yellowish fluorescence (F). Bars indicate lengths (10 µm). b Plates G–I and J–L show the absence of iNOS fluorescence in Wistar control islets (H, K). c NOS activities in freshly isolated islets. NO production from ncNOS, iNOS and total NOS in freshly isolated islets from Wistar control rats (open bars) and GK rats (hatched bars). Values are mean±s.e.m for n = 4–6 animals. *P<0.05; *** P<0.001
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pone-0002165-g001: a Confocal microscopy of islets directly isolated ex vivo from the GK rat. The islets were double-immunolabelled for insulin or glucagon and iNOS and analysed by confocal microscopy. Insulin staining and iNOS staining appear, respectively, as red (A) and green (B) fluorescence. Co-localization of insulin/iNOS is seen as orange-yellowish fluorescence (C). Similarly glucagon staining and iNOS staining appear, respectively, as red (D) and green (E) fluorescence. Co-localization of glucagon/iNOS is seen as orange-yellowish fluorescence (F). Bars indicate lengths (10 µm). b Plates G–I and J–L show the absence of iNOS fluorescence in Wistar control islets (H, K). c NOS activities in freshly isolated islets. NO production from ncNOS, iNOS and total NOS in freshly isolated islets from Wistar control rats (open bars) and GK rats (hatched bars). Values are mean±s.e.m for n = 4–6 animals. *P<0.05; *** P<0.001

Mentions: To investigate whether isolated islets express iNOS protein we performed a confocal microscopic study in GK islets. Islets were simultaneously immunolabeled for insulin or glucagon to investigate β- and α-cell specific expression of iNOS. As shown in Fig. 1a, immunoreactivity for iNOS was detected in insulin immunoreactive β-cells (A–C) and in glucagon immunoreactive α-cells (D–F) (orange-yellowish fluorescence in the overlay pictures). No iNOS immunoreactivity was found in Wistar control islets (Fig. 1b). Insulin immunoreactive β-cells (G–I) and glucagons immunoreactive α-cells (J–L) are shown.


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 Confocal microscopy of islets directly isolated ex vivo from the GK rat. The islets were double-immunolabelled for insulin or glucagon and iNOS and analysed by confocal microscopy. Insulin staining and iNOS staining appear, respectively, as red (A) and green (B) fluorescence. Co-localization of insulin/iNOS is seen as orange-yellowish fluorescence (C). Similarly glucagon staining and iNOS staining appear, respectively, as red (D) and green (E) fluorescence. Co-localization of glucagon/iNOS is seen as orange-yellowish fluorescence (F). Bars indicate lengths (10 µm). b Plates G–I and J–L show the absence of iNOS fluorescence in Wistar control islets (H, K). c NOS activities in freshly isolated islets. NO production from ncNOS, iNOS and total NOS in freshly isolated islets from Wistar control rats (open bars) and GK rats (hatched bars). Values are mean±s.e.m for n = 4–6 animals. *P<0.05; *** P<0.001
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2367446&req=5

pone-0002165-g001: a Confocal microscopy of islets directly isolated ex vivo from the GK rat. The islets were double-immunolabelled for insulin or glucagon and iNOS and analysed by confocal microscopy. Insulin staining and iNOS staining appear, respectively, as red (A) and green (B) fluorescence. Co-localization of insulin/iNOS is seen as orange-yellowish fluorescence (C). Similarly glucagon staining and iNOS staining appear, respectively, as red (D) and green (E) fluorescence. Co-localization of glucagon/iNOS is seen as orange-yellowish fluorescence (F). Bars indicate lengths (10 µm). b Plates G–I and J–L show the absence of iNOS fluorescence in Wistar control islets (H, K). c NOS activities in freshly isolated islets. NO production from ncNOS, iNOS and total NOS in freshly isolated islets from Wistar control rats (open bars) and GK rats (hatched bars). Values are mean±s.e.m for n = 4–6 animals. *P<0.05; *** P<0.001
Mentions: To investigate whether isolated islets express iNOS protein we performed a confocal microscopic study in GK islets. Islets were simultaneously immunolabeled for insulin or glucagon to investigate β- and α-cell specific expression of iNOS. As shown in Fig. 1a, immunoreactivity for iNOS was detected in insulin immunoreactive β-cells (A–C) and in glucagon immunoreactive α-cells (D–F) (orange-yellowish fluorescence in the overlay pictures). No iNOS immunoreactivity was found in Wistar control islets (Fig. 1b). Insulin immunoreactive β-cells (G–I) and glucagons immunoreactive α-cells (J–L) are shown.

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