Proinsulin C-peptide-mediated signalling and the search for its receptor
Proinsulin connecting pe... more Proinsulin C-peptide-mediated signalling and the search for its receptor Proinsulin connecting peptide (C-peptide) joins the A and B-chain of proinsulin and plays an important role in coordinating the folding of insulin. For many years this peptide was simply considered an inert by-product of insulin biosynthesis and was used mainly as an alternative marker for insulin secretion. Recent evidence, however, demonstrates convincingly that C-peptide has biological function and establishes C-peptide as an attractive therapeutic agent to provide protection against chronic diabetic complications. Little is known about C-peptide signalling in pancreatic cells with studies focussing on antioxidant effects. C-peptide could have protective roles in these cells. For example, pancreatic cells exposed to immune complexes in type 2 diabetes require protection possibly via C-peptide. Data presented here demonstrate that C-peptide induced a concentration-dependent phosphorylation (activation) of rpS6, at S235/S236 and S240/244, as well as phosphorylation of components of the upstream signalling pathways of rpS6 (ERK1/2, Akt and S6K) in the pancreatic cell line, INS-1E. C-peptide also caused concentration-dependent increases in phospo-ERK1/2 and phospho-rpS6 (S240/244) in HEK293 and SH-SY5Y, but not in HEK293A. Stimulatory effects of C-peptide on two important intracellular signalling pathways, ERK1/2 and rpS6, can deliver cytoprotective effects and may, therefore, be of potential importance in the treatment of diabetes. A major limitation of current work on C-peptide is that the receptor(s) have not been identified convincingly. Some recent evidence suggests that the orphan GPCR, GPR146, may be the C-peptide receptor. Here, stable overexpression of C-terminally EGFP-tagged GPR146 in HEK293 and HEK293A cells showed predominant membrane localisation of the receptor. However, C-peptide responses in these were unaffected and C-peptide-evoked internalisation/co-localisation of GPR146-EGFP was not observed. An expression cloning approach in Xenopus oocytes was used to screen pools of cDNA library clones for Gi-evoked responses of C-peptide given the pertussis toxin sensitivity of responses. This approach did not, however, reveal any C-peptide-evoked responses in any of the approximately 130,000 clones screened. Furthermore, the published C-peptide receptor candidates, GPR146 and -enolase did not respond to C-peptide when expressed in oocytes. Taken together, signalling events in a pancreatic cell line suggest relevance of C-peptide to events such as cell survival and proliferation. However, the present work provides no evidence that GPR146 is the C-peptide receptor, which still remains elusive.
Azilsartan, a known angiotensin receptor blocker, has shown potential in reducing 24-hour blood p... more Azilsartan, a known angiotensin receptor blocker, has shown potential in reducing 24-hour blood pressure and may have protective effects against cardiac complications. Increased oxidative stress in cardiac tissue is directly related to the cardiac complications of doxorubicin. This study investigated whether azilsartan could mitigate doxorubicin-induced cardiotoxicity. We divided 28 male rats into four groups: the control group receiving a standard diet and water, the vehicle group given DMSO orally for two weeks, doxorubicin group receiving 2.5 mg/kg of doxorubicin three times a week for two weeks, and azilsartan group treated with 5 mg/kg/day of azilsartan orally and doxorubicin. Doxorubicin-induced cardiotoxicity was evidenced by a significant increase in TNF-α, IL-1β, MDA, and caspase-3 levels and significantly decreased TAC and Bcl-2 levels in the cardiac tissues of treated rats compared to the DMSO and control groups. Azilsartan significantly decreased doxorubicin-induced cardiotoxicity, as evidenced by a decline in serum levels of both TNF-α and IL-1β. Additionally, MDA significantly decreased in the cardiac tissue, although TAC was significantly increased when comparing the azilsartan group to the group receiving doxorubicin-only. These results suggest that azilsartan effectively reduced doxorubicin-induced cardiotoxicity, likely by mitigating apoptosis, inflammation, and oxidative stress in cardiac tissues.
This study aimed to investigate the potential of nebivolol in preventing doxorubicin-induced card... more This study aimed to investigate the potential of nebivolol in preventing doxorubicin-induced cardiotoxicity by targeting the inflammatory, oxidative, and apoptotic pathways. Twenty-eight male rats were randomly divided into four groups, each consisting of seven rats. The control group received standard diets and unrestricted access to water. The rats in the normal saline (N/S) group were administered a 0.9% normal saline solution for two weeks. The doxorubicin group (the "induced group") received doxorubicin at a dosage of 2.5 mg/kg three times per week for two weeks. The nebivolol group received an oral dose of 4 mg/kg of nebivolol for the same duration. The cardiac tissues of rats treated with doxorubicin exhibited increased levels of tumor necrosis factor, interleukin-1, malondialdehyde, and caspase-3 compared to the normal saline control group (p<0.05), along with decreased levels of total antioxidant capacity and Bcl-2. These results show that doxorubicin is harmful to the heart. The administration of nebivolol significantly reduced the cardiotoxic effects induced by doxorubicin, as indicated by a statistically significant decrease in the levels of inflammatory markers, specifically tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β) (p<0.05). The nebivolol group exhibited a significant decrease in malondialdehyde levels, which serves as a signal of oxidation, in cardiac tissue compared to the doxorubicin-only group (p<0.05). Additionally, the nebivolol group showed a significant increase in overall antioxidant capacity. Nebivolol dramatically attenuated doxorubicin-induced cardiotoxicity in rats, likely by interfering with oxidative stress, the inflammatory response, and the apoptotic pathway.
Objective: Study investigates erythropoietin's nephroprotective effect in adult male rats wit... more Objective: Study investigates erythropoietin's nephroprotective effect in adult male rats with renal ischemia and reperfusion injury, examining biochemical parameters and renal tissue alterations. Methods: twenty-eight male rats of Sprague Dawley randomized into four groups: Sham, Iscemia/Reperfusion, NS, and Erythropoietin. Sham group treated kidneys identically without clamping pedicles. Ischemia/Reperfusion group underwent midline laparotomy, 30 minutes ischemia, 2 hours reperfusion, Rats received NS vehicle for Erythropoietin 30 minutes before ischemia, Erythropoietin dose administered 30 minutes before ischemia/reperfusion. Operation performed under maintained anesthesia using ketamine and xylazine injections. Results: Renal ischemia /reperfusion increased serum Cr, BUN, IL-1β, NF-kB, Caspase-3, while SOD, GSH, Bcl-2 decreased in induced rats. Erythropoietin treatment reduced Cr and BUN levels, Reduced inflammation, and inflammatory markers. Renal tissue antioxidant markers...
Dipyridamole is a platelet inhibitor with antithrombotic properties that can help prevent stroke ... more Dipyridamole is a platelet inhibitor with antithrombotic properties that can help prevent stroke recurrence. Twenty-eight male rats were divided randomly into four groups (7 rats in each group). Control group: rats received a natural diet and water. Normal saline group: rats received 0.9% normal saline for two weeks. Doxorubicin group (induced group): rats received 2.5 mg/kg three times a week for two weeks. Dipyridamole group (dipyridamole treated group): received dipyridamole (6 mg/kg/daily) orally for two weeks. Doxorubicin caused cardiotoxicity as indicated by a significant increase in tumor necrosis factor-α, interleukin-6, malondialdehyde, and caspase-3 level (P<0.05), while total antioxidant capacity and Bcl-2 levels were significantly reduced in cardiac tissues of rats in the doxorubicin group compared to the normal saline control group (P<0.05). Dipyridamole significantly ameliorates doxorubicin-induced cardiotoxicity, as suggested by a significant decrease in inflamm...
Objective: To evaluate the potential protective effect of irbesartan on atherosclerotic progressi... more Objective: To evaluate the potential protective effect of irbesartan on atherosclerotic progression using rosuvastatin as a positive control. Methods: Twenty local domestic rabbits were randomly divided into four groups, five rabbits per each group. The first group (I), rabbits were receiving normal diet; the second group (II), rabbits were receiving 2 % cholesterol diet; the third group (III), rabbits were receiving rosuvastatin and 2% cholesterol diet and; the fourth group (IV), rabbit were receiving irbesartan and 2% cholesterol diet. Serum level of cholesterol, triglycerides, LDL, VLDL and HDL were determined after 12 weeks of the study. Serum level of high sensitive C-reactive protein, ICAM1and VCAM1 were measured after 12 weeks of the study. Total antioxidant activity was also determined. Aortic tissue sent for histopathological examination of atherosclerosis lesion. Result: Data of this study have showed that atherogenic diet caused an increase in serum level of TC, LDL, VLDL...
The study aims to design and evaluate oral insulin for the purpose of achieving the following cri... more The study aims to design and evaluate oral insulin for the purpose of achieving the following criteria: effectiveness in controlling blood sugar when taking insulin orally, palatability of the oral dose characteristics in terms of shape, color, smell and taste to be acceptable, especially for children. Stability of oral insulin against intestinal metabolism achieves constant bioavailability as well as oral doses are eligible to all diabetic patients. The oral nano polymer insulin (NPI) was assessed by GC mass, FTIR, electrophoresis, melting point, fluorescence labeling, microscopy, calorimetric, albumin binding assay and hydrophobicity test. The overall in vivo findings showed that NPI had onset of action 35+15 min and 5+1.5 hr duration of action with oral efficacy of 34+4% of that for intraperitoneal (IP) route. The pharmaceutical properties were convenient for oral use.
Chronic obstructive pulmonary disease (COPD) is a group of common medical disorders. Morbidity an... more Chronic obstructive pulmonary disease (COPD) is a group of common medical disorders. Morbidity and mortality rate of this disease are increasing due to lack of both effective treatment and full understanding of pathogenesis and mechanism of this disease. Thus, current study aims to investigate the relationship between the expression of toll-like receptor 4 (TLR4) and BODE index in patient with COPD as a part of potential mechanism in the developing of COPD. This study is a case control study conducted in both Alsadar and Almerjan hospitals. A total of 187 individuals 87 patients with COPD and 100 people without COPD) were selected after application of inclusion and exclusion criteria. Using RT-PCR, the expression of TLR4 was investigated. FEV1/FVCratio was examined using spirometry. There was a significant decrease in the expression of TLR4 among COPD patients when compared with healthy individuals (P < 0.001). COPD patients showed a significant increase in BODE index when compar...
Atherosclerosis is a disorder of vasculature wall resulting mainly from the inflammatory processe... more Atherosclerosis is a disorder of vasculature wall resulting mainly from the inflammatory processes. This condition involves vascular endothelial dysfunction, recruitment and activation of phagocytic cells in early stages. Omega-3 polyunsaturated fatty acids comprise part of the cellular membrane function many roles including increased development and functionality of neuronal synapses. This study assesses the significance of omega-3 fatty acids on atherosclerosis events via lowering oxidative and inflammatory insults. In this study, twenty-four domestic rabbits (male) were randomly distributed into three groups. The first one was the negative control group in which, rabbits were received normal diet (Oxide) for twelve week-period. The second group was the hypercholesteremia-induced, untreated rabbits fed with cholesterol (1%) enriched diet. The third group consumed cholesterol (1%) enriched diet supplemented with 5% omega-3 fatty acids. Blood samples were collected after twelve week...
s: Janabi A, Ennion SJ, Willars GB (2016) C-peptide induces ribosomal protein S6 phosphorylation ... more s: Janabi A, Ennion SJ, Willars GB (2016) C-peptide induces ribosomal protein S6 phosphorylation in the pancreatic β-cell line, INS-1E has been accepted for the publication on pA2 Online.
Hemorrhagic shock followed by resuscitation is conceived as an insult frequently induces a system... more Hemorrhagic shock followed by resuscitation is conceived as an insult frequently induces a systemic inflammatory response syndrome and oxidative stress that results in multiple-organ dysfunction syndrome including acute lung injury. MK-886 is a leukotriene biosynthesis inhibitor exerts an anti inflammatory and antioxidant activity. The objective of present study was to assess the possible protective effect of MK-886 against hemorrhagic shock-induced acute lung injury via interfering with inflammatory and oxidative pathways. Eighteen adult Albino rats were assigned to three groups each containing six rats: group I, sham group, rats underwent all surgical instrumentation but neither hemorrhagic shock nor resuscitation was done; group II, Rats underwent hemorrhagic shock (HS) for 1 hr then resuscitated with Ringer's lactate (1 hr) (induced untreated group, HS); group III, HS + MK-886 (0.6 mg/kg i.p. injection 30 min before the induction of HS, and the same dose was repeated just be...
Proinsulin C-peptide-mediated signalling and the search for its receptor
Proinsulin connecting pe... more Proinsulin C-peptide-mediated signalling and the search for its receptor Proinsulin connecting peptide (C-peptide) joins the A and B-chain of proinsulin and plays an important role in coordinating the folding of insulin. For many years this peptide was simply considered an inert by-product of insulin biosynthesis and was used mainly as an alternative marker for insulin secretion. Recent evidence, however, demonstrates convincingly that C-peptide has biological function and establishes C-peptide as an attractive therapeutic agent to provide protection against chronic diabetic complications. Little is known about C-peptide signalling in pancreatic cells with studies focussing on antioxidant effects. C-peptide could have protective roles in these cells. For example, pancreatic cells exposed to immune complexes in type 2 diabetes require protection possibly via C-peptide. Data presented here demonstrate that C-peptide induced a concentration-dependent phosphorylation (activation) of rpS6, at S235/S236 and S240/244, as well as phosphorylation of components of the upstream signalling pathways of rpS6 (ERK1/2, Akt and S6K) in the pancreatic cell line, INS-1E. C-peptide also caused concentration-dependent increases in phospo-ERK1/2 and phospho-rpS6 (S240/244) in HEK293 and SH-SY5Y, but not in HEK293A. Stimulatory effects of C-peptide on two important intracellular signalling pathways, ERK1/2 and rpS6, can deliver cytoprotective effects and may, therefore, be of potential importance in the treatment of diabetes. A major limitation of current work on C-peptide is that the receptor(s) have not been identified convincingly. Some recent evidence suggests that the orphan GPCR, GPR146, may be the C-peptide receptor. Here, stable overexpression of C-terminally EGFP-tagged GPR146 in HEK293 and HEK293A cells showed predominant membrane localisation of the receptor. However, C-peptide responses in these were unaffected and C-peptide-evoked internalisation/co-localisation of GPR146-EGFP was not observed. An expression cloning approach in Xenopus oocytes was used to screen pools of cDNA library clones for Gi-evoked responses of C-peptide given the pertussis toxin sensitivity of responses. This approach did not, however, reveal any C-peptide-evoked responses in any of the approximately 130,000 clones screened. Furthermore, the published C-peptide receptor candidates, GPR146 and -enolase did not respond to C-peptide when expressed in oocytes. Taken together, signalling events in a pancreatic cell line suggest relevance of C-peptide to events such as cell survival and proliferation. However, the present work provides no evidence that GPR146 is the C-peptide receptor, which still remains elusive.
Azilsartan, a known angiotensin receptor blocker, has shown potential in reducing 24-hour blood p... more Azilsartan, a known angiotensin receptor blocker, has shown potential in reducing 24-hour blood pressure and may have protective effects against cardiac complications. Increased oxidative stress in cardiac tissue is directly related to the cardiac complications of doxorubicin. This study investigated whether azilsartan could mitigate doxorubicin-induced cardiotoxicity. We divided 28 male rats into four groups: the control group receiving a standard diet and water, the vehicle group given DMSO orally for two weeks, doxorubicin group receiving 2.5 mg/kg of doxorubicin three times a week for two weeks, and azilsartan group treated with 5 mg/kg/day of azilsartan orally and doxorubicin. Doxorubicin-induced cardiotoxicity was evidenced by a significant increase in TNF-α, IL-1β, MDA, and caspase-3 levels and significantly decreased TAC and Bcl-2 levels in the cardiac tissues of treated rats compared to the DMSO and control groups. Azilsartan significantly decreased doxorubicin-induced cardiotoxicity, as evidenced by a decline in serum levels of both TNF-α and IL-1β. Additionally, MDA significantly decreased in the cardiac tissue, although TAC was significantly increased when comparing the azilsartan group to the group receiving doxorubicin-only. These results suggest that azilsartan effectively reduced doxorubicin-induced cardiotoxicity, likely by mitigating apoptosis, inflammation, and oxidative stress in cardiac tissues.
This study aimed to investigate the potential of nebivolol in preventing doxorubicin-induced card... more This study aimed to investigate the potential of nebivolol in preventing doxorubicin-induced cardiotoxicity by targeting the inflammatory, oxidative, and apoptotic pathways. Twenty-eight male rats were randomly divided into four groups, each consisting of seven rats. The control group received standard diets and unrestricted access to water. The rats in the normal saline (N/S) group were administered a 0.9% normal saline solution for two weeks. The doxorubicin group (the "induced group") received doxorubicin at a dosage of 2.5 mg/kg three times per week for two weeks. The nebivolol group received an oral dose of 4 mg/kg of nebivolol for the same duration. The cardiac tissues of rats treated with doxorubicin exhibited increased levels of tumor necrosis factor, interleukin-1, malondialdehyde, and caspase-3 compared to the normal saline control group (p<0.05), along with decreased levels of total antioxidant capacity and Bcl-2. These results show that doxorubicin is harmful to the heart. The administration of nebivolol significantly reduced the cardiotoxic effects induced by doxorubicin, as indicated by a statistically significant decrease in the levels of inflammatory markers, specifically tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β) (p<0.05). The nebivolol group exhibited a significant decrease in malondialdehyde levels, which serves as a signal of oxidation, in cardiac tissue compared to the doxorubicin-only group (p<0.05). Additionally, the nebivolol group showed a significant increase in overall antioxidant capacity. Nebivolol dramatically attenuated doxorubicin-induced cardiotoxicity in rats, likely by interfering with oxidative stress, the inflammatory response, and the apoptotic pathway.
Objective: Study investigates erythropoietin's nephroprotective effect in adult male rats wit... more Objective: Study investigates erythropoietin's nephroprotective effect in adult male rats with renal ischemia and reperfusion injury, examining biochemical parameters and renal tissue alterations. Methods: twenty-eight male rats of Sprague Dawley randomized into four groups: Sham, Iscemia/Reperfusion, NS, and Erythropoietin. Sham group treated kidneys identically without clamping pedicles. Ischemia/Reperfusion group underwent midline laparotomy, 30 minutes ischemia, 2 hours reperfusion, Rats received NS vehicle for Erythropoietin 30 minutes before ischemia, Erythropoietin dose administered 30 minutes before ischemia/reperfusion. Operation performed under maintained anesthesia using ketamine and xylazine injections. Results: Renal ischemia /reperfusion increased serum Cr, BUN, IL-1β, NF-kB, Caspase-3, while SOD, GSH, Bcl-2 decreased in induced rats. Erythropoietin treatment reduced Cr and BUN levels, Reduced inflammation, and inflammatory markers. Renal tissue antioxidant markers...
Dipyridamole is a platelet inhibitor with antithrombotic properties that can help prevent stroke ... more Dipyridamole is a platelet inhibitor with antithrombotic properties that can help prevent stroke recurrence. Twenty-eight male rats were divided randomly into four groups (7 rats in each group). Control group: rats received a natural diet and water. Normal saline group: rats received 0.9% normal saline for two weeks. Doxorubicin group (induced group): rats received 2.5 mg/kg three times a week for two weeks. Dipyridamole group (dipyridamole treated group): received dipyridamole (6 mg/kg/daily) orally for two weeks. Doxorubicin caused cardiotoxicity as indicated by a significant increase in tumor necrosis factor-α, interleukin-6, malondialdehyde, and caspase-3 level (P<0.05), while total antioxidant capacity and Bcl-2 levels were significantly reduced in cardiac tissues of rats in the doxorubicin group compared to the normal saline control group (P<0.05). Dipyridamole significantly ameliorates doxorubicin-induced cardiotoxicity, as suggested by a significant decrease in inflamm...
Objective: To evaluate the potential protective effect of irbesartan on atherosclerotic progressi... more Objective: To evaluate the potential protective effect of irbesartan on atherosclerotic progression using rosuvastatin as a positive control. Methods: Twenty local domestic rabbits were randomly divided into four groups, five rabbits per each group. The first group (I), rabbits were receiving normal diet; the second group (II), rabbits were receiving 2 % cholesterol diet; the third group (III), rabbits were receiving rosuvastatin and 2% cholesterol diet and; the fourth group (IV), rabbit were receiving irbesartan and 2% cholesterol diet. Serum level of cholesterol, triglycerides, LDL, VLDL and HDL were determined after 12 weeks of the study. Serum level of high sensitive C-reactive protein, ICAM1and VCAM1 were measured after 12 weeks of the study. Total antioxidant activity was also determined. Aortic tissue sent for histopathological examination of atherosclerosis lesion. Result: Data of this study have showed that atherogenic diet caused an increase in serum level of TC, LDL, VLDL...
The study aims to design and evaluate oral insulin for the purpose of achieving the following cri... more The study aims to design and evaluate oral insulin for the purpose of achieving the following criteria: effectiveness in controlling blood sugar when taking insulin orally, palatability of the oral dose characteristics in terms of shape, color, smell and taste to be acceptable, especially for children. Stability of oral insulin against intestinal metabolism achieves constant bioavailability as well as oral doses are eligible to all diabetic patients. The oral nano polymer insulin (NPI) was assessed by GC mass, FTIR, electrophoresis, melting point, fluorescence labeling, microscopy, calorimetric, albumin binding assay and hydrophobicity test. The overall in vivo findings showed that NPI had onset of action 35+15 min and 5+1.5 hr duration of action with oral efficacy of 34+4% of that for intraperitoneal (IP) route. The pharmaceutical properties were convenient for oral use.
Chronic obstructive pulmonary disease (COPD) is a group of common medical disorders. Morbidity an... more Chronic obstructive pulmonary disease (COPD) is a group of common medical disorders. Morbidity and mortality rate of this disease are increasing due to lack of both effective treatment and full understanding of pathogenesis and mechanism of this disease. Thus, current study aims to investigate the relationship between the expression of toll-like receptor 4 (TLR4) and BODE index in patient with COPD as a part of potential mechanism in the developing of COPD. This study is a case control study conducted in both Alsadar and Almerjan hospitals. A total of 187 individuals 87 patients with COPD and 100 people without COPD) were selected after application of inclusion and exclusion criteria. Using RT-PCR, the expression of TLR4 was investigated. FEV1/FVCratio was examined using spirometry. There was a significant decrease in the expression of TLR4 among COPD patients when compared with healthy individuals (P < 0.001). COPD patients showed a significant increase in BODE index when compar...
Atherosclerosis is a disorder of vasculature wall resulting mainly from the inflammatory processe... more Atherosclerosis is a disorder of vasculature wall resulting mainly from the inflammatory processes. This condition involves vascular endothelial dysfunction, recruitment and activation of phagocytic cells in early stages. Omega-3 polyunsaturated fatty acids comprise part of the cellular membrane function many roles including increased development and functionality of neuronal synapses. This study assesses the significance of omega-3 fatty acids on atherosclerosis events via lowering oxidative and inflammatory insults. In this study, twenty-four domestic rabbits (male) were randomly distributed into three groups. The first one was the negative control group in which, rabbits were received normal diet (Oxide) for twelve week-period. The second group was the hypercholesteremia-induced, untreated rabbits fed with cholesterol (1%) enriched diet. The third group consumed cholesterol (1%) enriched diet supplemented with 5% omega-3 fatty acids. Blood samples were collected after twelve week...
s: Janabi A, Ennion SJ, Willars GB (2016) C-peptide induces ribosomal protein S6 phosphorylation ... more s: Janabi A, Ennion SJ, Willars GB (2016) C-peptide induces ribosomal protein S6 phosphorylation in the pancreatic β-cell line, INS-1E has been accepted for the publication on pA2 Online.
Hemorrhagic shock followed by resuscitation is conceived as an insult frequently induces a system... more Hemorrhagic shock followed by resuscitation is conceived as an insult frequently induces a systemic inflammatory response syndrome and oxidative stress that results in multiple-organ dysfunction syndrome including acute lung injury. MK-886 is a leukotriene biosynthesis inhibitor exerts an anti inflammatory and antioxidant activity. The objective of present study was to assess the possible protective effect of MK-886 against hemorrhagic shock-induced acute lung injury via interfering with inflammatory and oxidative pathways. Eighteen adult Albino rats were assigned to three groups each containing six rats: group I, sham group, rats underwent all surgical instrumentation but neither hemorrhagic shock nor resuscitation was done; group II, Rats underwent hemorrhagic shock (HS) for 1 hr then resuscitated with Ringer's lactate (1 hr) (induced untreated group, HS); group III, HS + MK-886 (0.6 mg/kg i.p. injection 30 min before the induction of HS, and the same dose was repeated just be...
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Proinsulin connecting peptide (C-peptide) joins the A and B-chain of proinsulin and plays an important role in coordinating the folding of insulin. For many years this peptide was simply considered an inert by-product of insulin biosynthesis and was used mainly as an alternative marker for insulin secretion. Recent evidence, however, demonstrates convincingly that C-peptide has biological function and establishes C-peptide as an attractive therapeutic agent to provide protection against chronic diabetic complications. Little is known about C-peptide signalling in pancreatic cells with studies focussing on antioxidant effects. C-peptide could have protective roles in these cells. For example, pancreatic cells exposed to immune complexes in type 2 diabetes require protection possibly via C-peptide. Data presented here demonstrate that C-peptide induced a concentration-dependent phosphorylation (activation) of rpS6, at S235/S236 and S240/244, as well as phosphorylation of components of the upstream signalling pathways of rpS6 (ERK1/2, Akt and S6K) in the pancreatic cell line, INS-1E. C-peptide also caused concentration-dependent increases in phospo-ERK1/2 and phospho-rpS6 (S240/244) in HEK293 and SH-SY5Y, but not in HEK293A. Stimulatory effects of C-peptide on two important intracellular signalling pathways, ERK1/2 and rpS6, can deliver cytoprotective effects and may, therefore, be of potential importance in the treatment of diabetes. A major limitation of current work on C-peptide is that the receptor(s) have not been identified convincingly. Some recent evidence suggests that the orphan GPCR, GPR146, may be the C-peptide receptor. Here, stable overexpression of C-terminally EGFP-tagged GPR146 in HEK293 and HEK293A cells showed predominant membrane localisation of the receptor. However, C-peptide responses in these were unaffected and C-peptide-evoked internalisation/co-localisation of GPR146-EGFP was not observed. An expression cloning approach in Xenopus oocytes was used to screen pools of cDNA library clones for Gi-evoked responses of C-peptide given the pertussis toxin sensitivity of responses. This approach did not, however, reveal any C-peptide-evoked responses in any of the approximately 130,000 clones screened. Furthermore, the published C-peptide receptor candidates, GPR146 and -enolase did not respond to C-peptide when expressed in oocytes. Taken together, signalling events in a pancreatic cell line suggest relevance of C-peptide to events such as cell survival and proliferation. However, the present work provides no evidence that GPR146 is the C-peptide receptor, which still remains elusive.
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Proinsulin connecting peptide (C-peptide) joins the A and B-chain of proinsulin and plays an important role in coordinating the folding of insulin. For many years this peptide was simply considered an inert by-product of insulin biosynthesis and was used mainly as an alternative marker for insulin secretion. Recent evidence, however, demonstrates convincingly that C-peptide has biological function and establishes C-peptide as an attractive therapeutic agent to provide protection against chronic diabetic complications. Little is known about C-peptide signalling in pancreatic cells with studies focussing on antioxidant effects. C-peptide could have protective roles in these cells. For example, pancreatic cells exposed to immune complexes in type 2 diabetes require protection possibly via C-peptide. Data presented here demonstrate that C-peptide induced a concentration-dependent phosphorylation (activation) of rpS6, at S235/S236 and S240/244, as well as phosphorylation of components of the upstream signalling pathways of rpS6 (ERK1/2, Akt and S6K) in the pancreatic cell line, INS-1E. C-peptide also caused concentration-dependent increases in phospo-ERK1/2 and phospho-rpS6 (S240/244) in HEK293 and SH-SY5Y, but not in HEK293A. Stimulatory effects of C-peptide on two important intracellular signalling pathways, ERK1/2 and rpS6, can deliver cytoprotective effects and may, therefore, be of potential importance in the treatment of diabetes. A major limitation of current work on C-peptide is that the receptor(s) have not been identified convincingly. Some recent evidence suggests that the orphan GPCR, GPR146, may be the C-peptide receptor. Here, stable overexpression of C-terminally EGFP-tagged GPR146 in HEK293 and HEK293A cells showed predominant membrane localisation of the receptor. However, C-peptide responses in these were unaffected and C-peptide-evoked internalisation/co-localisation of GPR146-EGFP was not observed. An expression cloning approach in Xenopus oocytes was used to screen pools of cDNA library clones for Gi-evoked responses of C-peptide given the pertussis toxin sensitivity of responses. This approach did not, however, reveal any C-peptide-evoked responses in any of the approximately 130,000 clones screened. Furthermore, the published C-peptide receptor candidates, GPR146 and -enolase did not respond to C-peptide when expressed in oocytes. Taken together, signalling events in a pancreatic cell line suggest relevance of C-peptide to events such as cell survival and proliferation. However, the present work provides no evidence that GPR146 is the C-peptide receptor, which still remains elusive.