Chronic constipation and treatment options (Review)

  • Authors:
    • Magdy El‑Salhy
    • Rune Svensen
    • Jan Gunnar Hatlebakk
    • Odd‑Helge Gilja
    • Trygve Hausken
  • View Affiliations

  • Published online on: November 4, 2013     https://doi.org/10.3892/mmr.2013.1770
  • Pages: 3-8
Metrics: Total Views: 0 (Spandidos Publications: | PMC Statistics: )
Total PDF Downloads: 0 (Spandidos Publications: | PMC Statistics: )


Abstract

Chronic constipation (CC) is a highly prevalent heterogeneous disorder. Although CC is not known to be associated with the development of serious disease or with excess mortality, it considerably reduces the patients quality of life. In addition, it represents an economic burden to patients and society. The majority of patients with CC successfully manage the disorder by dietary management and the use of laxatives. Patients with functional CC (slow‑transit and non‑slow transit constipation) do not respond to laxatives and are a small fraction of the total population complaining of constipation. Regardless of the low number of these patients, the intractability of their symptoms causes psychological and social stress and greatly impairs their quality of life. Furthermore, these patients consume a disproportionate quantity of medical resources. It appears that these patients have a disturbance in the serotonin transmission system, which results in a cascade of alterations in a number of gut neuroendocrine hormones/transmitters. The effect of prucalopride, a serotonin receptor agonist, in this category of patients appears to be not only a pharmacological prokinetic action, but also a correction of a pre‑existing disturbance. Linaclotide, a member of the guanylin peptide family, binds to the ligand‑binding region of guanylate cyclase‑C on the luminal surface of gastrointestinal epithelia resulting in increased fluid secretion. This drug has also been found to be effective for the treatment of functional CC. In addition, biofeedback and sacral nerve stimulation are effective in the treatment of CC caused by pelvic floor disorders.

1. Introduction

Chronic constipation (CC) is a highly prevalent heterogeneous disorder. The prevalence of CC varies based on how the disorder is defined and whether CC is self-reported or based on criteria (15) (Fig. 1). The prevalence rates for females are almost double those for males. CC is not known to be associated with the development of serious disease or with excess mortality rate. However, CC considerably reduces the quality of life to the same degree or more severe than impairments caused by a number of other chronic diseases, including arthritis, asthma or coronary artery disease (69). CC is commonly associated with anxiety and depression worldwide (1012).

In addition to the increased morbidity caused by CC, it is an economic burden to the patients and society. Significant economic costs in CC arise from direct and indirect costs. The direct costs are associated with evaluation and treatment and the indirect costs are caused by missing school or work (absenteeism) or not being as productive at school or work as usual (presenteeism). CC led to 6.3 million patient visits in the US in 2004 (13,14). A large survey study found that the annual health care costs for patients with CC were US$7522 per patient, ~50% higher compared with patients with irritable bowel syndrome (IBS; US$5049 per patient) (11). The long-term direct medical costs of CC are double those of controls over a 15-year period (US$63,591 vs. $24,529) (15). In England, 14 million prescriptions were issued for laxatives per year at a cost of £60 million (1).

2. Definition and types of constipation

Constipation is a complex symptom that may be clinically grouped into infrequent bowel movements (<3 per week) and difficult defecation, including straining at defecation, hard or lumpy stools, sensation of incomplete evacuation, sensation of blockage or anorectal obstruction and manual manoeuvres to defecation.

As mentioned previously, patients with CC are a heterogonous group and may be roughly divided into 3 groups: i) Constipation in the elderly and cancer patients; ii) constipation associated with neuromuscular diseases and iii) functional constipation.

Constipation in the elderly and cancer patients constitutes the majority of CC patients. Neither motility disturbances in the gastrointestinal tract or abnormalities in the gut neuroendocrine system have been described to be associated with aging (1618). It appears that constipation in the elderly is caused primarily by co-morbidity and the side effects of drugs, particularly those used against cardiovascular diseases. In cancer patients, constipation is caused mainly by opiates.

Patients with neuromuscular diseases, including Parkinson’s disease, multiple sclerosis and amyotrophic lateral sclerosis suffer from chronic constipation, which is treated differently.

Functional CC comprises idiopathic chronic slow transit constipation and severe forms of IBS. A number of gastroenterologists, including the authors, believe that they are variants of the same disorder (19).

3. Possible mechanisms for functional constipation

A number of abnormalities in the neuroendocrine system (NES) of the gut have been observed in slow transit and non-slow transit (IBS-constipation?) (2030). The gut NES is a local regulatory system, that controls numerous functions of the gastrointestinal tract, including motility, secretion, absorption, gut microcirculation, local immune defence and cell proliferation. It consists of two parts: i) Endocrine cells spread between the epithelial cells of the mucosa facing the gut lumen and ii) peptidergic, serotonergic and nitric-oxide-containing nerves of the enteric nervous system in the gut wall. The gut NES is operated by a large number of bioactive messengers that exert their effects via endocrine, paracrine and neuroendocrine modes of action or by synaptic signalling (31,32). The different components of this system interact and integrate with each other and with the afferent and efferent nerve fibres of the central nervous system (33,34).

In slow and non-slow transit constipation low colonic serotonin and peptide YY (PYY) cell densities and low serotonin content have been observed (24,26,30,33) (Figs. 2 and 3). Serotonin activates the submucosal sensory branch of the enteric nervous system (32,34), which conveys sensations to the central nervous system that are likely to generate the sensation of abdominal pain/discomfort. Furthermore, serotonin controls gastrointestinal motility and chloride secretion via interneurons and motor neurons (31,34). PYY stimulates the absorption of water and electrolytes and is a major regulator of the ‘ileal brake’. Furthermore, PYY inhibits prostaglandin E2 and vasoactive intestinal polypeptides, which stimulate intestinal fluid secretion (32,34). Administration of PYY inhibits diarrhoea in experimental mouse models by reducing intestinal fluid secretion and slowing colonic transit (32,34). It appears that functional CC patients have a disturbance in the serotonin transmission system, which causes a cascade of changes in a number of gut neuroendocrine hormones/transmitters, the most important of which is PYY.

4. Treatment options

The European guidelines recommend a treatment algorithm for CC (Fig. 4) (35). The drugs used for the treatment of constipation are summarized in Table I.

Table I

The most common types of drugs used for the treatment of patients with chronic constipation.

Table I

The most common types of drugs used for the treatment of patients with chronic constipation.

Drug classGeneric nameCommentsDose
Bulking agentsPsylliumEffective25–30 g daily in divided doses
IspaghulaEffective3.5 g one to three times daily
Osmotic laxativePolyethylene glycolEffective
Unpalatable taste17 g in 237 ml solution daily
LactuloseEffective
May cause bloating, flatulence and cramping15–30 ml (667 mg/ml) daily
Stimulant laxativesBisacodylEffective, but the effects subside with time, can cause cramping5–20 mg daily
Natrium bicosulfate5–10 mg daily
Emollient laxativeMineral oilEffective5–10 cm3 daily
Glycerine suppositoriesEffective
Initiates evacuation by distending the rectumOn demand
Prokinetic and prosecretory agentsPrucloprideEffective. May cause headache, nausea, abdominal pain and diarrhoea.
These adverse events occur within the first 24 h of treatment and are short lived
2 mg daily
LinaclotideEffective
Diarrhea is the most common side effect290 μg daily

Non-pharmacological and changes in life style are the first approaches in the management of mild and moderate constipation. Guidance of diet management with an emphasis on an increase in soluble fibre intake appears to be effective in patients with mild and moderate constipation (35). Based on clinical experience and circumstantial evidence, physicians recommend exercise for CC patients. The physical activity effects on CC patients have previously been attributed to promoting overall wellbeing. However, physical activity has been found recently to increase gastrointestinal transit (3639). The increased gastrointestinal motility has been attributed to vagus stimulation and/or decreased blood flow to the gut, which leads to an increase in important gastrointestinal hormone release (39). Probiotic intake has also been shown to improve CC symptoms depending on the preparation used and a number of products appear to be more effective than others (4044). The bacteria that have been proven to be effective in this aspect are Bifidobacterium infantis 35624, Bifidobacterium lactis DN-173-010, Lactobacillus plantrum, Lactobacillus rhamnosus, Lactobacillus acidophilus and Streptococcus faecium(4144). The mechanism that appears to underlie this improvement is the ability of these bacteria to reduce the number of sulphite-reducing Clostridia spp., which is known to produce gas upon the fermentation of nutrients. This may contribute to improvements in flatulence, bloating and abdominal distension in CC patients (42). Combining diet management, regular exercise and probiotics intake has been found to be effective in reducing the symptoms and improving the quality of life in CC patients with mild and moderate symptoms (45).

In the elderly, concomitant drug use should be assessed and drugs that potentially cause constipation should be discontinued, when possible. Constipation in the elderly and in cancer patients is treated successfully by using one or more of the following bulking agents; polyethylene glycol, lactulose, sodium bicosulphate and bisacodyl. Probiotic intake reduces the side effects of lactulose and fibres. CC in patients with neuromuscular diseases is successfully treated with polyethylene glycol.

Patients with functional CC do not respond to any of the laxatives mentioned previously. They are a small fraction of the total population complaining of constipation (46). Regardless of the low number of these patients, the intractability of their symptoms causes psychological and social stress and greatly impairs their quality of life. Furthermore, they consume a disproportionate quantity of medical resources. The treatment options for these patients are prucalopride, linaclotide, biofeedback and sacral nerve stimulation.

Prucalopride is a highly selective serotonin 5HT4 receptor agonist that has been shown to stimulate gut motility (47). It has been observed to be effective in the treatment of CC that does not respond to laxatives (4751). Furthermore, it is safe for use in the elderly who commonly suffer from cardiovascular diseases (4751). As mentioned previously, patients with CC have low serotonin content in the large intestine and it is possible that the effects of prucalopride, a serotonin receptor agonist in this category of patients is not only a pharmacological prokinetic effect, but also a correction of a pre-existing defect in serotonin.

Linaclotide is a member of the guanylin peptide family and similar to endogenous peptide hormones, guanylin and uroguanylinhas have been shown to bind to the ligand binding region of guanylate cyclase-C on the luminal surface of gastrointestinal epithelia, resulting in increased fluid secretion (52). Moreover, linaclotide has been observed to accelerate gastrointestinal transit (52) and has been found to be effective in the treatment of functional CC.

Biofeedback and sacral nerve stimulation have a limited availability and content of biofeedback treatment varies among centers. These treatments are effective in constipation caused by pelvic floor disorders, but the author’s observations and recently published reports showed that this treatment is not effective in functional constipation (53).

5. Conclusion

CC is a common gastrointestinal disorder with different aethiology. It markedly reduces the patient’s quality of life and is an economic burden to the patients and society. The majority of patients are treated successfully with changes in life style, bulking agents or other laxatives. Patients with functional CC who do not respond to the treatment with laxatives may be treated with prucaloprid or linaclotide. Patients with CC caused by pelvic floor disorders may be successfully treated by biofeedback or sacral nerve stimulation

References

1 

Woodward S: Assessment and management of constipation in older people. Nurs Older People. 24:21–26. 2012. View Article : Google Scholar : PubMed/NCBI

2 

Pare P: The approach to diagnosis and treatment of chronic constipation: suggestions for a general practitioner. Can J Gastroenterol. 25(Suppl B): 36B–40B. 2011.PubMed/NCBI

3 

Lacy BE, Levenick JM and Crowell M: Chronic constipation: new diagnostic and treatment approaches. Therap Adv Gastroenterol. 5:233–247. 2012. View Article : Google Scholar : PubMed/NCBI

4 

Peppas G, Alexiou VG, Mourtzoukou E and Falagas ME: Epidemiology of constipation in Europe and Oceania: a systematic review. BMC Gastroenterol. 8:52008. View Article : Google Scholar : PubMed/NCBI

5 

Sanchez MI and Bercik P: Epidemiology and burden of chronic constipation. Can J Gastroenterol. 25(Suppl B): 11B–15B. 2011.PubMed/NCBI

6 

Irvine EJ, Ferrazzi S, Pare P, Thompson WG and Rance L: Health-related quality of life in functional GI disorders: focus on constipation and resource utilization. Am J Gastroenterol. 97:1986–1993. 2002.PubMed/NCBI

7 

Sun SX, Dibonaventura M, Purayidathil FW, Wagner JS, Dabbous O and Mody R: Impact of chronic constipation on health-related quality of life, work productivity, and healthcare resource use: an analysis of the National Health and Wellness Survey. Dig Dis Sci. 56:2688–2695. 2011.PubMed/NCBI

8 

Everhart JE and Ruhl CE: Burden of digestive diseases in the United States part II: lower gastrointestinal diseases. Gastroenterology. 136:741–754. 2009. View Article : Google Scholar : PubMed/NCBI

9 

Sandler RS, Everhart JE, Donowitz M, et al: The burden of selected digestive diseases in the United States. Gastroenterology. 122:1500–1511. 2002. View Article : Google Scholar : PubMed/NCBI

10 

Cheng C, Chan AO, Hui WM and Lam SK: Coping strategies, illness perception, anxiety and depression of patients with idiopathic constipation: a population-based study. Aliment Pharmacol Ther. 18:319–326. 2003. View Article : Google Scholar : PubMed/NCBI

11 

Mason HJ, Serrano-Ikkos E and Kamm MA: Psychological state and quality of life in patients having behavioral treatment (biofeedback) for intractable constipation. Am J Gastroenterol. 97:3154–3159. 2002. View Article : Google Scholar : PubMed/NCBI

12 

Haug TT, Mykletun A and Dahl AA: Are anxiety and depression related to gastrointestinal symptoms in the general population? Scand J Gastroenterol. 37:294–298. 2002. View Article : Google Scholar : PubMed/NCBI

13 

Martin BC, Barghout V and Cerulli A: Direct medical costs of constipation in the United States. Managed care interface. 19:43–49. 2006.PubMed/NCBI

14 

Nyrop KA, Palsson OS, Levy RL, et al: Costs of health care for irritable bowel syndrome, chronic constipation, functional diarrhoea and functional abdominal pain. Aliment Pharmacol Ther. 26:237–248. 2007. View Article : Google Scholar : PubMed/NCBI

15 

Choung RS, Branda ME, Chitkara D, et al: Longitudinal direct medical costs associated with constipation in women. Aliment Pharmacol Ther. 33:251–260. 2011. View Article : Google Scholar : PubMed/NCBI

16 

McCrea GL, Miaskowski C, Stotts NA, Macera L and Varma MG: Pathophysiology of constipation in the older adult. World J Gastroenterol. 14:2631–2638. 2008. View Article : Google Scholar : PubMed/NCBI

17 

Sandström O and El-Salhy M: Ageing and endocrine cells of human duodenum. Mech Ageing Dev. 108:39–48. 1999.

18 

Sandström O and El-Salhy M: Human rectal endocrine cells and aging. Mech Ageing Dev. 108:219–226. 1999.PubMed/NCBI

19 

Quigley EM: Prucalopride: safety, efficacy and potential applications. Therap Adv Gastroenterol. 5:23–30. 2012. View Article : Google Scholar : PubMed/NCBI

20 

Krishnamurthy S, Schuffler MD, Rohrmann CA and Pope CE II: Severe idiopathic constipation is associated with a distinctive abnormality of the colonic myenteric plexus. Gastroenterology. 88:26–34. 1985. View Article : Google Scholar : PubMed/NCBI

21 

Schouten WR, ten Kate FJ, de Graaf EJ, Gilberts EC, Simons JL and Klück P: Visceral neuropathy in slow transit constipation: an immunohistochemical investigation with monoclonal antibodies against neurofilament. Dis Colon Rectum. 36:1112–1117. 1993. View Article : Google Scholar

22 

Wedel T, Roblick UJ, Ott V, et al: Oligoneuronal hypoganglionosis in patients with idiopathic slow-transit constipation. Dis Colon Rectum. 45:54–62. 2002. View Article : Google Scholar : PubMed/NCBI

23 

Park HJ, Kamm MA, Abbasi AM and Talbot IC: Immunohistochemical study of the colonic muscle and innervation in idiopathic chronic constipation. Dis Colon Rectum. 38:509–513. 1995. View Article : Google Scholar : PubMed/NCBI

24 

El-Salhy M and Norrgård O: Colonic neuroendocrine peptide levels in patients with chronic idiopathic slow transit constipation. Ups J Med Sci. 103:223–230. 1998. View Article : Google Scholar : PubMed/NCBI

25 

Sjölund K, Ekman R, Akre F and Lindner P: Motilin in chronic idiopathic constipation. Scand J Gastroenterol. 21:914–918. 1986.

26 

Sjölund K, Fasth S, Ekman R, et al: Neuropeptides in idiopathic chronic constipation (slow transit constipation). Neurogastroenterol Motil. 9:143–150. 1997.PubMed/NCBI

27 

Preston DM, Adrian TE, Christofides ND, Lennard-Jones JE and Bloom SR: Positive correlation between symptoms and circulating motilin, pancreatic polypeptide and gastrin concentrations in functional bowel disorders. Gut. 26:1059–1064. 1985. View Article : Google Scholar

28 

Tomita R, Fujisaki S, Ikeda T and Fukuzawa M: Role of nitric oxide in the colon of patients with slow-transit constipation. Dis Colon Rectum. 45:593–600. 2002. View Article : Google Scholar : PubMed/NCBI

29 

Tomita R, Tanjoh K, Fujisaki S, Ikeda T and Fukuzawa M: Regulation of the enteric nervous system in the colon of patients with slow transit constipation. Hepatogastroenterol. 49:1540–1544. 2002.

30 

El-Salhy M, Norrgård O and Spinnell S: Abnormal colonic endocrine cells in patients with chronic idiopathic slow-transit constipation. Scand J Gastroenterol. 34:1007–1011. 1999. View Article : Google Scholar : PubMed/NCBI

31 

El-Salhy M, Ostgaard H, Gundersen D, Hatlebakk JG and Hausken T: The role of diet in the pathogenesis and management of irritable bowel syndrome (Review). Int J Mol Med. 29:723–731. 2012.PubMed/NCBI

32 

El-Salhy M, Seim I, Chopin L, Gundersen D, Hatlebakk JG and Hausken T: Irritable bowel syndrome: the role of gut neuroendocrine peptides. Front Biosci (Elite Ed). 4:2783–2800. 2012. View Article : Google Scholar : PubMed/NCBI

33 

El-Salhy M, Gundersen D, Ostgaard H, Lomholt-Beck B, Hatlebakk JG and Hausken T: Low densities of serotonin and peptide YY cells in the colon of patients with irritable bowel syndrome. Dig Dis Sci. 57:873–878. 2012. View Article : Google Scholar : PubMed/NCBI

34 

El-Salhy M, Gundersen D, Hatlebakk JG and Hausken T: Irritable Bowel Syndrome: Diagnosis, Pathogenesis and Treatment Options. 1st edition. Nova Science Publishers, Inc; New York: 2012

35 

Tack J, Müller-Lissner S, Stanghellini V, et al: Diagnosis and treatment of chronic constipation - a European perspective. Neurogastroenterol Motil. 23:697–710. 2011. View Article : Google Scholar

36 

Ostgaard H, Hausken T, Gundersen D and El-Salhy M: Diet and effects of diet management on quality of life and symptoms in patients with irritable bowel syndrome. Mol Med Rep. 5:1382–1390. 2012.PubMed/NCBI

37 

Johannesson E, Simrén M, Strid H, Bajor A and Sadik R: Physical activity improves symptoms in irritable bowel syndrome: a randomized controlled trial. Am J Gastroenterol. 106:915–922. 2011. View Article : Google Scholar : PubMed/NCBI

38 

Chey WD and Rai J: Exercise and IBS: no pain, no gain. Gastroenterology. 141:1941–1943. 2011. View Article : Google Scholar : PubMed/NCBI

39 

Strid H, Simrén M, Störsrud S, Stotzer PO and Sadik R: Effect of heavy exercise on gastrointestinal transit in endurance athletes. Scand J Gastroenterol. 46:673–677. 2011. View Article : Google Scholar : PubMed/NCBI

40 

Wang Y, Kondo T, Suzukamo Y, Oouchida Y and Izumi S: Vagal nerve regulation is essential for the increase in gastric motility in response to mild exercise. Tohoku J Exp Med. 222:155–163. 2010. View Article : Google Scholar : PubMed/NCBI

41 

Whelan K: Probiotics and prebiotics in the management of irritable bowel syndrome: a review of recent clinical trials and systematic reviews. Curr Opin Clin Nutr Metab Care. 14:581–587. 2011. View Article : Google Scholar : PubMed/NCBI

42 

Whorwell PJ: Do probiotics improve symptoms in patients with irritable bowel syndrome? Therap Adv Gastroenterol. 2:37–44. 2009. View Article : Google Scholar : PubMed/NCBI

43 

Spiller R: Review article: probiotics and prebiotics in irritable bowel syndrome. Aliment Pharmacol Ther. 28:385–396. 2008. View Article : Google Scholar : PubMed/NCBI

44 

Aragon G, Graham DB, Borum M and Doman DB: Probiotic therapy for irritable bowel syndrome. Gastroenterol Hepatol (NY). 6:39–44. 2010.PubMed/NCBI

45 

El-Salhy M, Lillebø E, Reinemo A, Salmelid L and Hausken T: Effects of a health program comprising reassurance, diet management, probiotics administration and regular exercise on symptoms and quality of life in patients with irritable bowel syndrome. Gastroenterology Insights. 2:21–26. 2010. View Article : Google Scholar

46 

Spiller RC: Upper gut dysmotility in slow-transit constipation: is it evidence for a pan-enteric neurological deficit in severe slow transit constipation? Eur J Gastroenterol Hepatol. 11:693–696. 1999. View Article : Google Scholar : PubMed/NCBI

47 

Quigley EM, Vandeplassche L, Kerstens R and Ausma J: Clinical trial: the efficacy, impact on quality of life, and safety and tolerability of prucalopride in severe chronic constipation - a 12-week, randomized, double-blind, placebo-controlled study. Aliment Pharmacol Ther. 29:315–328. 2009. View Article : Google Scholar : PubMed/NCBI

48 

Tack J, Camilleri M, Chang L, et al: Systematic review: cardiovascular safety profile of 5-HT(4) agonists developed for gastrointestinal disorders. Aliment Pharmacol Ther. 35:745–767. 2012. View Article : Google Scholar : PubMed/NCBI

49 

Ke M, Zou D, Yuan Y, et al: Prucalopride in the treatment of chronic constipation in patients from the Asia-Pacific region: a randomized, double-blind, placebo-controlled study. Neurogastroenterol Motil. 24:999–e541. 2012. View Article : Google Scholar : PubMed/NCBI

50 

Camilleri M, Van Outryve MJ, Beyens G, Kerstens R, Robinson P and Vandeplassche L: Clinical trial: the efficacy of open-label prucalopride treatment in patients with chronic constipation - follow-up of patients from the pivotal studies. Aliment Pharmacol Ther. 32:1113–1123. 2010. View Article : Google Scholar : PubMed/NCBI

51 

Camilleri M, Beyens G, Kerstens R, Robinson P and Vandeplassche L: Safety assessment of prucalopride in elderly patients with constipation: a double-blind, placebo-controlled study. Neurogastroenterol Motil. 21:1256–e1117. 2009. View Article : Google Scholar : PubMed/NCBI

52 

Johnston JM, Shiff SJ and Quigley EM: A review of the clinical efficacy of linaclotide in irritable bowel syndrome with constipation. Curr Med Res Opin. 29:149–160. 2013. View Article : Google Scholar : PubMed/NCBI

53 

Emmanuel A: Current management strategies and therapeutic targets in chronic constipation. Therap Adv Gastroenterol. 4:37–48. 2011. View Article : Google Scholar : PubMed/NCBI

Related Articles

Journal Cover

2014-January
Volume 9 Issue 1

Print ISSN: 1791-2997
Online ISSN:1791-3004

Sign up for eToc alerts

Recommend to Library

Copy and paste a formatted citation
x
Spandidos Publications style
El‑Salhy M, Svensen R, Hatlebakk JG, Gilja OH and Hausken T: Chronic constipation and treatment options (Review). Mol Med Rep 9: 3-8, 2014
APA
El‑Salhy, M., Svensen, R., Hatlebakk, J.G., Gilja, O., & Hausken, T. (2014). Chronic constipation and treatment options (Review). Molecular Medicine Reports, 9, 3-8. https://doi.org/10.3892/mmr.2013.1770
MLA
El‑Salhy, M., Svensen, R., Hatlebakk, J. G., Gilja, O., Hausken, T."Chronic constipation and treatment options (Review)". Molecular Medicine Reports 9.1 (2014): 3-8.
Chicago
El‑Salhy, M., Svensen, R., Hatlebakk, J. G., Gilja, O., Hausken, T."Chronic constipation and treatment options (Review)". Molecular Medicine Reports 9, no. 1 (2014): 3-8. https://doi.org/10.3892/mmr.2013.1770