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Can specific calcium channel blockade be the basis for a drug-based treatment of acute pancreatitis? Ole Petersen
a
a
Cardiff University – Cardiff School of Biosciences, The Sir Martin Evans Building Museum Avenue, Cardiff CF10 3AX, UK Published online: 27 Mar 2015.
Click for updates To cite this article: Ole Petersen (2014) Can specific calcium channel blockade be the basis for a drug-based treatment of acute pancreatitis?, Expert Review of Gastroenterology & Hepatology, 8:4, 339-341 To link to this article: http://dx.doi.org/10.1586/17474124.2014.896192
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Editorial
Can specific calcium channel blockade be the basis for a drug-based treatment of acute pancreatitis? Expert Rev. Gastroenterol. Hepatol. 8(4), 339–341 (2014)
Downloaded by [UNSW Library] at 14:52 24 August 2015
Ole Petersen Cardiff University – Cardiff School of Biosciences, The Sir Martin Evans Building Museum Avenue, Cardiff CF10 3AX, UK [email protected]
Acute pancreatitis is an inflammatory disease with a significant mortality, triggered by autodigestion and cell death. There is currently no specific treatment. Excessive intracellular Ca2+ signals, elicited by combinations of fat and alcohol or bile acids, initiate the intracellular protease activation that causes autodigestion. These abnormal Ca2+ signals are generated by excessive Ca2+ release from internal stores followed by excessive Ca2+ influx from the interstitial fluid. The intracellular protease activation is totally dependent on sustained Ca2+ influx. It has recently been shown that the influx pathway belongs to the CRAC (Ca2+ release activated Ca2+) channel type. A selective blocker is now available for this channel and recent work, reviewed in this editorial, shows that pharmacological blockade in isolated pancreatic acinar cells, prevents the excessive Ca2+ signal generation, intracellular protease activation and necrosis that is the root cause of acute pancreatitis. This gives hope for a rational treatment of this disease.
Acute pancreatitis (AP) is an inflammatory disease in which the normally inactive digestive proenzymes become active enzymes inside the manufacturing acinar cells, causing autodigestion and cell death [1]. AP is the leading cause of hospital admissions for gastrointestinal disorders (>270,000 admissions due to AP per year in the USA alone; 30% increase from 2000 to 2009), and there is a significant mortality with more than 3000 deaths per year due to AP in the USA alone [2]. Repeated attacks of AP may lead to chronic pancreatitis, increasing – by a factor of 10–100 – the risk of developing pancreatic cancer, which is the second leading cause of gastrointestinal cancer deaths (>35,000 deaths due to pancreatic cancer per year in the USA) [2]. There is currently no specific drug-based treatment for AP. The main causes of AP are alcohol abuse and biliary disease, but hypertriglyceridemia and hypercalcemia are also known to trigger AP [1,3]. There is now substantial evidence for the hypothesis, first advanced in 1995 [4], that abnormal
intracellular Ca2+ signaling is the initial trigger of AP and that excessive Ca2+ release from stores inside acinar cells, followed by excessive Ca2+ entry from the interstitial fluid, increases intracellular protease activity causing pancreatic acinar cell necrosis [4–7]. This, in turn, will cause a major inflammatory response worsening the disease [1]. Current treatments of AP are supportive (including pain control and management of fluid balance) [3], but do not deal with the root cause of the disease, namely the intracellular protease activation initiated and maintained by excessive Ca2+ signal generation in the acinar cells, which is evoked by, for example, alcohol metabolites or bile acids [1]. However, there are now opportunities for therapeutic intervention in the early stages of the disease, which have only recently come into view as our understanding of Ca2+ handling in the pancreatic acinar cells has matured. Early work on stimulus–secretion coupling in salivary glands and the pancreas revealed that the initial event following
KEYWORDS: acute pancreatitis • calcium channel blockade • calcium signalling • necrosis • protease activity
informahealthcare.com
10.1586/17474124.2014.896192
2014 Informa UK Ltd
ISSN 1747-4124
339
Downloaded by [UNSW Library] at 14:52 24 August 2015
Editorial
Petersen
physiological stimulation of the acinar cells was release of Ca2+ stored in intracellular organelles and that Ca2+ influx from the extracellular fluid occurred thereafter [8,9]. We now know that both physiological and pathological stimulation of the pancreatic acinar cells release Ca2+ from the endoplasmic reticulum (ER), primarily via inositol 1,4,5-trisphosphate (IP3) receptors, but also to some extent via ryanodine receptors, and that the reduction in the intrastore Ca2+ concentration causes opening of Ca2+ channels in the plasma membrane, mediating the sustained Ca2+ entry into the cells during prolonged stimulation [8,9]. In addition, it is now clear that the intracellular Ca2+releasing messengers IP3, cyclic ADP-ribose and nicotinic acid adenine dinucleotide phosphate can all release Ca2+ also from the secretory (zymogen) granules and probably other acid intracellular Ca2+ stores [8]. More recent studies of the Ca2+ transport events initiated by pancreatitis-inducing stimulants, including alcohol, nonoxidative products of alcohol and fatty acids (fatty acid ethyl esters [FAEEs]), as well as bile acids, showed that all these agents liberate Ca2+ from both the ER and acidic stores and that the Ca2+ release from the acid stores also proceeds mainly through IP3 receptors [4,5]. It is the release of Ca2+ from the acid stores rather than the ER that is specifically linked to the initial intracellular protease activation, although Ca2+ entry, governed by release of Ca2+ from the ER (store-operated Ca2+ entry), is required to sustain it [4–6]. Knockout of type 2 IP3 receptors markedly reduces FAEEinduced intracellular Ca2+ release as well as trypsinogen activation and double knockout of both types 2 and 3 IP3 receptors further reduces Ca2+ release and trypsinogen activation to very low levels [5]. This most likely indicates that the magnitude of the intracellular Ca2+ release determines the extent of the initial trypsinogen activation. We do not yet understand the molecular mechanism by which ethanol, FAEEs and bile acids open IP3 receptors, but we know that the intracellular Ca2+-binding protein calmodulin protects against excessive Ca2+ release and trypsinogen activation [4,10]. A potential therapy could be built on this by exploiting the calmodulin-activating property of certain Ca2+-like peptides [4,10]. Although there are opportunities for developing potential therapies against AP by targeting the primary intracellular Ca2+ release process [4,10], it may be more profitable to focus on the subsequent sustained Ca2+ entry process as this would not necessarily depend on getting drugs into the intracellular compartment. In fact, inhibition of the opening of Ca2+ entry channels has been successful in the treatment of other diseases. Although voltage-gated Ca2+ channels perform vitally important functions in many different tissues, including neurons, muscle and endocrine glands, it has been clear for a long time that therapies based on inhibiting specific types of such channels are viable. Indeed, various types of blockers of voltage-gated Ca2+ channels have for many years had a secure place in cardiovascular medicine [11]. However, it has been known since the earliest days of stimulus–secretion coupling studies in exocrine glands that the pancreatic acinar cells do not possess voltage-gated Ca2+ channels and that unlike, for example, the situation in the 340
neighboring insulin-secreting b-cells, membrane depolarization does not evoke secretion [4]. In order to assess the potential of Ca2+ channel blockers as therapeutic agents in the treatment of AP, it is necessary to know the properties of the Ca2+ influx channels. Store-operated Ca2+ entry pathways in pancreatic acinar cells include TRPC3 channels, which are nonselective cation channels [12,13]. The opening of these channels can be inhibited by pyrazole 3, and it has been suggested that a therapy against AP could be developed based on the action of this agent [12,13]. However, TRPC3 channels are probably not the major part of the storeoperated Ca2+ influx pathway in the acinar cells, because the TRPC3 inhibitor pyrazole 3 or knockout of TRPC3 channels only caused a reduction in the inward current following Ca2+ store depletion to about 60% of the control level. Similar results were obtained when store-operated Ca2+ entry was assessed by cytosolic Ca2+ measurements [12,13]. Nevertheless, such inhibition of TRPC3 channels did reduce trypsinogen activation and the severity of pancreatitis-like changes in the tissue [12,13]. In a more recent study of store-operated Ca2+ influx and Ca2+ entry currents in pancreatic acinar cells, it was shown that the main pathway is a ‘classical’ Ca2+ release-activated Ca2+ (CRAC) current [6]. In this study, the Ca2+ currents were measured directly and a clear time course relationship established between the gradual emptying of the intracellular stores and the gradual activation of the inward Ca2+ current. The inward current was uninfluenced by removal of external Na+, but very sensitive to changes in the external Ca2+ concentration, indicating its Ca2+-selective nature [6]. The relatively selective CRAC channel blocker GSK7975A [14] evoked acutely a marked reduction in the fully developed CRAC current to
Expert Review of Gastroenterology & Hepatology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/ierh20
Can specific calcium channel blockade be the basis for a drug-based treatment of acute pancreatitis? Ole Petersen
a
a
Cardiff University – Cardiff School of Biosciences, The Sir Martin Evans Building Museum Avenue, Cardiff CF10 3AX, UK Published online: 27 Mar 2015.
Click for updates To cite this article: Ole Petersen (2014) Can specific calcium channel blockade be the basis for a drug-based treatment of acute pancreatitis?, Expert Review of Gastroenterology & Hepatology, 8:4, 339-341 To link to this article: http://dx.doi.org/10.1586/17474124.2014.896192
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Editorial
Can specific calcium channel blockade be the basis for a drug-based treatment of acute pancreatitis? Expert Rev. Gastroenterol. Hepatol. 8(4), 339–341 (2014)
Downloaded by [UNSW Library] at 14:52 24 August 2015
Ole Petersen Cardiff University – Cardiff School of Biosciences, The Sir Martin Evans Building Museum Avenue, Cardiff CF10 3AX, UK [email protected]
Acute pancreatitis is an inflammatory disease with a significant mortality, triggered by autodigestion and cell death. There is currently no specific treatment. Excessive intracellular Ca2+ signals, elicited by combinations of fat and alcohol or bile acids, initiate the intracellular protease activation that causes autodigestion. These abnormal Ca2+ signals are generated by excessive Ca2+ release from internal stores followed by excessive Ca2+ influx from the interstitial fluid. The intracellular protease activation is totally dependent on sustained Ca2+ influx. It has recently been shown that the influx pathway belongs to the CRAC (Ca2+ release activated Ca2+) channel type. A selective blocker is now available for this channel and recent work, reviewed in this editorial, shows that pharmacological blockade in isolated pancreatic acinar cells, prevents the excessive Ca2+ signal generation, intracellular protease activation and necrosis that is the root cause of acute pancreatitis. This gives hope for a rational treatment of this disease.
Acute pancreatitis (AP) is an inflammatory disease in which the normally inactive digestive proenzymes become active enzymes inside the manufacturing acinar cells, causing autodigestion and cell death [1]. AP is the leading cause of hospital admissions for gastrointestinal disorders (>270,000 admissions due to AP per year in the USA alone; 30% increase from 2000 to 2009), and there is a significant mortality with more than 3000 deaths per year due to AP in the USA alone [2]. Repeated attacks of AP may lead to chronic pancreatitis, increasing – by a factor of 10–100 – the risk of developing pancreatic cancer, which is the second leading cause of gastrointestinal cancer deaths (>35,000 deaths due to pancreatic cancer per year in the USA) [2]. There is currently no specific drug-based treatment for AP. The main causes of AP are alcohol abuse and biliary disease, but hypertriglyceridemia and hypercalcemia are also known to trigger AP [1,3]. There is now substantial evidence for the hypothesis, first advanced in 1995 [4], that abnormal
intracellular Ca2+ signaling is the initial trigger of AP and that excessive Ca2+ release from stores inside acinar cells, followed by excessive Ca2+ entry from the interstitial fluid, increases intracellular protease activity causing pancreatic acinar cell necrosis [4–7]. This, in turn, will cause a major inflammatory response worsening the disease [1]. Current treatments of AP are supportive (including pain control and management of fluid balance) [3], but do not deal with the root cause of the disease, namely the intracellular protease activation initiated and maintained by excessive Ca2+ signal generation in the acinar cells, which is evoked by, for example, alcohol metabolites or bile acids [1]. However, there are now opportunities for therapeutic intervention in the early stages of the disease, which have only recently come into view as our understanding of Ca2+ handling in the pancreatic acinar cells has matured. Early work on stimulus–secretion coupling in salivary glands and the pancreas revealed that the initial event following
KEYWORDS: acute pancreatitis • calcium channel blockade • calcium signalling • necrosis • protease activity
informahealthcare.com
10.1586/17474124.2014.896192
2014 Informa UK Ltd
ISSN 1747-4124
339
Downloaded by [UNSW Library] at 14:52 24 August 2015
Editorial
Petersen
physiological stimulation of the acinar cells was release of Ca2+ stored in intracellular organelles and that Ca2+ influx from the extracellular fluid occurred thereafter [8,9]. We now know that both physiological and pathological stimulation of the pancreatic acinar cells release Ca2+ from the endoplasmic reticulum (ER), primarily via inositol 1,4,5-trisphosphate (IP3) receptors, but also to some extent via ryanodine receptors, and that the reduction in the intrastore Ca2+ concentration causes opening of Ca2+ channels in the plasma membrane, mediating the sustained Ca2+ entry into the cells during prolonged stimulation [8,9]. In addition, it is now clear that the intracellular Ca2+releasing messengers IP3, cyclic ADP-ribose and nicotinic acid adenine dinucleotide phosphate can all release Ca2+ also from the secretory (zymogen) granules and probably other acid intracellular Ca2+ stores [8]. More recent studies of the Ca2+ transport events initiated by pancreatitis-inducing stimulants, including alcohol, nonoxidative products of alcohol and fatty acids (fatty acid ethyl esters [FAEEs]), as well as bile acids, showed that all these agents liberate Ca2+ from both the ER and acidic stores and that the Ca2+ release from the acid stores also proceeds mainly through IP3 receptors [4,5]. It is the release of Ca2+ from the acid stores rather than the ER that is specifically linked to the initial intracellular protease activation, although Ca2+ entry, governed by release of Ca2+ from the ER (store-operated Ca2+ entry), is required to sustain it [4–6]. Knockout of type 2 IP3 receptors markedly reduces FAEEinduced intracellular Ca2+ release as well as trypsinogen activation and double knockout of both types 2 and 3 IP3 receptors further reduces Ca2+ release and trypsinogen activation to very low levels [5]. This most likely indicates that the magnitude of the intracellular Ca2+ release determines the extent of the initial trypsinogen activation. We do not yet understand the molecular mechanism by which ethanol, FAEEs and bile acids open IP3 receptors, but we know that the intracellular Ca2+-binding protein calmodulin protects against excessive Ca2+ release and trypsinogen activation [4,10]. A potential therapy could be built on this by exploiting the calmodulin-activating property of certain Ca2+-like peptides [4,10]. Although there are opportunities for developing potential therapies against AP by targeting the primary intracellular Ca2+ release process [4,10], it may be more profitable to focus on the subsequent sustained Ca2+ entry process as this would not necessarily depend on getting drugs into the intracellular compartment. In fact, inhibition of the opening of Ca2+ entry channels has been successful in the treatment of other diseases. Although voltage-gated Ca2+ channels perform vitally important functions in many different tissues, including neurons, muscle and endocrine glands, it has been clear for a long time that therapies based on inhibiting specific types of such channels are viable. Indeed, various types of blockers of voltage-gated Ca2+ channels have for many years had a secure place in cardiovascular medicine [11]. However, it has been known since the earliest days of stimulus–secretion coupling studies in exocrine glands that the pancreatic acinar cells do not possess voltage-gated Ca2+ channels and that unlike, for example, the situation in the 340
neighboring insulin-secreting b-cells, membrane depolarization does not evoke secretion [4]. In order to assess the potential of Ca2+ channel blockers as therapeutic agents in the treatment of AP, it is necessary to know the properties of the Ca2+ influx channels. Store-operated Ca2+ entry pathways in pancreatic acinar cells include TRPC3 channels, which are nonselective cation channels [12,13]. The opening of these channels can be inhibited by pyrazole 3, and it has been suggested that a therapy against AP could be developed based on the action of this agent [12,13]. However, TRPC3 channels are probably not the major part of the storeoperated Ca2+ influx pathway in the acinar cells, because the TRPC3 inhibitor pyrazole 3 or knockout of TRPC3 channels only caused a reduction in the inward current following Ca2+ store depletion to about 60% of the control level. Similar results were obtained when store-operated Ca2+ entry was assessed by cytosolic Ca2+ measurements [12,13]. Nevertheless, such inhibition of TRPC3 channels did reduce trypsinogen activation and the severity of pancreatitis-like changes in the tissue [12,13]. In a more recent study of store-operated Ca2+ influx and Ca2+ entry currents in pancreatic acinar cells, it was shown that the main pathway is a ‘classical’ Ca2+ release-activated Ca2+ (CRAC) current [6]. In this study, the Ca2+ currents were measured directly and a clear time course relationship established between the gradual emptying of the intracellular stores and the gradual activation of the inward Ca2+ current. The inward current was uninfluenced by removal of external Na+, but very sensitive to changes in the external Ca2+ concentration, indicating its Ca2+-selective nature [6]. The relatively selective CRAC channel blocker GSK7975A [14] evoked acutely a marked reduction in the fully developed CRAC current to
