Introduction
Asthma is a complex chronic inflammatory illness of the airways affecting 235 million people worldwide (WHO 2013). The disease is characterised by airway hyper-responsiveness (AHR), cellular inflammation and increased mucus production leading to airway obstruction (Moon et al. 2008, p. 275)(Abidi 2014, p. 19). Shahid and Khair-ul-Bariyah describes asthma as the increased contractibility of the tissue in the airways as a the result of an inflammatory process (2014, p. 215).
It became evident during this review that the inflammatory process of asthma is not fully understood and that studies are still being carried out. These studies are trying to map out which cells are involved in the inflammation of the airway smooth muscle cells (ASMC’s), and which of these processes should be inhibited for most effective relief of asthma symptoms (Tan et al. 2012, p. L700).
Turmeric has been used for centuries for its anti-inflammatory properties. The plants Latin name is Curcuma Longa and it originates in India and Asia. Historically turmeric has been used by Ayurveda practitioners for its healing properties (Kaviraj 1907, p. 332, 334, 355). In a more recent publication of Ayurveda medication Tirtha suggests turmeric in the treatment of asthma (1998, p. 88) unfortunately without describing the application.
When searching for literature for this review it became apparent that this research question is relatively un-chartered. Research into the validity of curcumin as an asthma treatment is still in the animal research stage. Only two studies on human participants were found, as a result no systematic reviews or meta-analyses were found.
Main findings
In vivo - animals
In the five studies on murine subjects, asthma was induced using the OVA method. This is where the subjects are first injected with ovalbumin to produce inflammation of the airways (Moon et al. 2008, p. 276). Methacholine is then injected to create asthma like symptoms. Curcumins effect on asthma is tested by measuring the airway hyper responsiveness (AHR). Different studies used slightly different methods.
Wang et al. used a method of dividing the subjects into five groups; four were induced with OVA and one control group received saline(2012, p. 3673). Out of the four OVA treated groups, one remained as a control group and didn’t receive any treatment; one received a placebo which tested the effect of the delivery method lipid nanoparticles but without curcumin; and two groups received curcumin. One of these groups received curcumin in lipid nanoparticles and the other received curcumin orally. All five groups’ AHR was tested. Both groups receiving curcumin showed attenuated AHR. The group receiving curcumin in lipid nanoparticles compared with 66% increase to the OVA control group and by 50% to the oral curcumin group. This study indicates that curcumin can be made very effective with the right delivery system.
In addition to Wang’s study, three of five murine studies measured AHR and report positive results after the application of curcumin.
Trials on human subjects
Only two studies on human subjects were found.
Kim et al. performed a small study on 15 subjects with asthma, where six subjects were given a placebo and nine were given 2000mg of curcumin per day ( 2011, p.51). This study measured the forced expiratory volume in 1 second (FEV1) of the subjects in 5 visits, with 30 days intervals. The results are presented as not having a statistical significance and further studies were recommended.
A slightly larger study was conducted by Abidi et al. (2014), where results from 60 subject were analysed. The subjects were randomly assigned to one of two groups. Group A received only standard asthma treatment, and Group B received standard asthma treatment plus 500mg curcumin capsules per day. FEV1 measured every 10 days for a month. Results showed an improvement of FEV1 and although more studies are recommended, the study concluded curcumin as a safe add-on therapy to standard asthma treatment.
In vitro studies
The methods of in vitro studies varied, but three studies looked at the suppression of Th2 cells. T helper 2 (Th2) cells and Th1 cells are present in the pulmonary tract and act as immune function helper cells. Asthma can be the result of an imbalance between these two cells (Jason Baker 2004, p. 81).
OVA induced asthma can exhibit as an upregulation of inflammatory regulators, which is when the Th2 increase the cytokines (Jang et al. 2014, p. 925). Jang et al. managed to decrease Th2 cells by 70% compared to the control group (2014, p. 928).
Another study by Chong et al. looked at how the Notch1 cell influences the balance between Th1 and Th2 cells. The study proved curcumins positive effect on OVA induced asthma on murine subjects, indicating that curcumin is a potential agent of preventing asthma (2015, p. 1483).
Zeng et al. proved that curcumin can inhibits proliferation of ASMCs, which gives us another new way of looking at the treatment of asthma (2013, p. 635). The results of this study indicate that the effects of an asthma attack can be significantly diminished with the application of curcumin(2013, p. 634).
All studies reported a clear in vitro improvement on the tissue treated with curcumin, compared to the tissue which was untreated. Zeng et al. found that regardless of the dosages, curcumin reduced the infiltration of inflammatory cells on the peribronchial areas (2013, p. 631).
Conclusion
With the complexity of the disease state and the current studies into the inflammatory cell function related to asthma, it is difficult to ascertain whether the laboratory studies reviewed could be used in a systematic review or meta-analysis. The test results were presented differently in each study and different parameters were tested.
The human studies were both very small; the smallest had poor validity due to size and the use of placebo. The other human study was well presented and seemed to have much better validity, but was still too small to be conclusive.
Could oral application be effective enough to replace standard asthma treatment, or should sophisticated delivery systems be developed? Two of the reviewed studies looked at different delivery systems; lipid nanoparticles (Wang et al. 2012) and a dry emulsion (Jang et al. 2014). Both of these showed 30-70% better results compared to oral application of dried curcumin. These studies were done by universities, sponsored by local government. The development of sophisticated delivery systems could be controversial for a naturally occurring remedy such as curcumin, which is freely available in ground turmeric. Sophisticated delivery systems create a profitable product, rather than a natural remedy which is accessible to all. Such big improvements in results due to delivery systems should be investigated further, to ensure the results were reported accurately.
This literature review found that curcumin has great potential to alleviate the symptoms of asthma; however this research is its infancy and although all studies showed positive results, it is conclusive that more studies are needed in this area.
References
Abidi, A 2014, ‘Evaluation of Efficacy of Curcumin as an Add-on therapy in Patients of Bronchial Asthma’, Journal of Clinical and Diagnostic Research, vol. 8, no. 8, pp. 19–24.
Chong, L, Zhang, W, Nie, Y, Yu, G, Liu, L, Lin, L, Wen, S, Zhu, L & Li, C 2015, ‘Protective Effect of Curcumin on Acute Airway Inflammation of Allergic Asthma in Mice Through Notch1–GATA3 Signaling Pathway’, Inflammation, vol. 37, no. 5, pp. 1476–1485, viewed 24 September 2015, <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4174331/>.
Jang, D-J, Kim, ST, Euichaul, O & Kooyeon, L 2014, ‘Enhanced oral bioavailability and antiasthmatic efficacy of curcumin using’, Bio-Medical Materials and Engineering, vol. 24, pp. 917–930, viewed 6 September 2015, <https://www-ebscohost-com.ezproxy.endeavour.edu.au/>.
Jason Baker, CM 2004, ‘The Inflammatory Process and Asthma’, Townsend Letter for Doctors and Patients, pp. 80–84, viewed 6 September 2015, <http://www.highbeam.com/doc/1G1-116179935.html>.
Kaviraj, KLB 1907, The Sushruta Samhita, vol. I, J.N. Bose, Calcutta, viewed 7 September 2015, <https://archive.org/details/englishtranslati01susruoft>.
Kim, D, Phillips, J & Lockey, R 2011, ‘Oral curcumin supplementation in patients with atopic asthma’, Allergy & Rhinology, vol. 2, no. 2, pp. 51–53.
Moon, DO, Kim, MO, Lee, HJ, Choi, YH, Park, YM, Heo, MS & Kim, GY 2008, ‘Curcumin attenuates ovalbumin-induced airway inflammation by regulating nitric oxide’, Biochemical and Biophysical Research Communications, vol. 375, no. 2, pp. 275–279.
Shahid, MT & Khair-ul-bariyah, S 2014, ‘Anti-Asthmatic and Cardioprotective Efficacy of Curcumin-A Review’, International Journal of Scientific Research in Knowledge, vol. 2, no. 5, pp. 215–223.
Tan, X, Khalil, N, Tesarik, C, Vanapalli, K, Yaputra, V, Alkhouri, H, Oliver, BGG, Armour, CL & Hughes, JM 2012, ‘Th1 cytokine-induced syndecan-4 shedding by airway smooth muscle cells is dependent on mitogen-activated protein kinases’, AJP: Lung Cellular and Molecular Physiology, vol. 302, no. 7, pp. L700–L710.
Tirtha, SSS 1998, The Ayurveda encyclopedia: Natural Secrets to Healing, Prevention, and Longevity, 1st edn, Ayurveda Holistic Center Press, Bayville, NY, USA, viewed 21 September 2015, <https://archive.org/stream/ayurvedaencyclop00tirt#page/n3/mode/2up>.
Wang, W, Zhu, R, Xie, Q, Li, A, Xiao, Y, Li, K, Liu, H, Cui, D, Chen, Y & Wang, S 2012, Enhanced bioavailability and efficiency of curcumin for the treatment of asthma by its formulation in solid lipid nanoparticles, International Journal of Nanomedicine, pp. 3667–3677.
WHO 2013, World Health Organization, viewed 24 September 2015, <http://www.who.int/mediacentre/factsheets/fs307/en/>.
Zeng, X, Cheng, Y, Qy, Y, Xu, J, Han, Z & Zhang, T 2013, ‘Curcumin inhibits the proliferation of airway smooth muscle cells in vitro and in vivo’, International Journal of Molecular Medicine, vol. 32, pp. 629–636.
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