Akrilik asit tabanlı polimerik hidrojellerden farklı vücut sıvılarını taklit eden ph ortamlarında antidiyabetik ilaç salınımı
Antidiabetic drug release from acrylic acid-based polymeric hydrojels in ph mediums mimicking different body fluids
Yazar: MELEK ÖZTÜRK
Danışman: PROF. DR. AYŞEGÜL GÖLCÜ ; DR. ÖĞR. ÜYESİ NEJLA ÇİNİ
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Kimya Ana Bilim Dalı / Kimya Bilim Dalı
Derece: Yüksek Lisans, 2023
Konu: Kimya = Chemistry
Dizin: Hidrojeller = Hydrogels ; Kontrollü ilaç salımı = Controlled drug release

Özet:
Kontrollü ilaç salım sistemleri, geleneksel yöntemlere göre ilaç dağıtmanın daha etkili bir yolunu sağlamak için geliştirilmiştir. Geleneksel yöntemlerdeki dar terapötik pencere, sık ve tekrarlayan dozlarda ilaç kullanımı gereksinimi ve istenmeyen yan etkiler gibi kısıtlayıcı etkiler sebebiyle etken maddenin vücuda veriliş yöntemlerinin iyileştirilmesi hayati önem taşımaktadır. Geliştirilen hidrojel sistemler etken maddenin vücuda verilmesi için kontrollü ilaç salımı çalışmalarında önemli bir yer tutmaktadır. Hidrojeller yapılarındaki fonksiyonel gruplar sayesinde çeşitli çevreselsel uyaranlara yanıt olarak şişme ve büzüşme davranışı gösteren yapılardır. Özellikle insan vücudunun değişen pH değerlerine sahip olması pH'a duyarlı hidrojellerin ilaç taşıyıcı sistemler olarak tercih edilmesine sebep olmuştur. 
Diyabet mellitus (DM) ülkemizde ve dünyada çok sık rastlanan endokrin bir hastalık türüdür ve diyabet vakalarının %90'dan fazlasını tip 2 DM (T2DM) oluşturmaktadır. Genellikle ileri yaşlarda ortaya çıkan hastalığın komplikasyonları nedeniyle ilaç sayısı oldukça fazla ve tedavi programı karmaşıktır. İlaç kullanımında ortaya çıkan; ilaçları zamanında almayı unutma, ilaçları karıştırma, ilaçları yanlış dozda alma ya da kendi kendine ilacı bırakma gibi hatalar ilaç tedavisinin etkinliğinin azalmasına sebep olmaktadır. Kontrollü ilaç salım sistemleri ile ilacın terapötik etkinliği arttırmak, ilaç konsantrasyonundaki dalgalanmaları ve ilacın yan etkilerini azaltmak tedavi için büyük önem taşımaktadır. 
Bu çalışmada, T2DM tedavisinde kullanılan antihiperglisemik ilaçlar olan Metformin Hidroklorür (MET∙HCl) ve Pioglitazon Hidroklorür (PİOG∙HCl) ile çalışılmıştır. Bu ilaç etken maddelerinin poli(akrilik asit) bazlı hidrojel sistemlerden salımı, 37°C'de temsili olarak hazırlanan mide sıvısı (pH:1,2), bağırsak sıvısı (pH:7,4) ve vücut sıvısı (pH:7,4) ortamlarında incelenmiştir. Ayrıca, hidrojellerin şişme derecesi ve salma kinetiği de karşılaştırılmıştır. Çapraz bağlayıcı konsantrasyonu ve ilaç konsantrasyonu yönünden kıyaslayabilmek açısından her bir ilaç için dört farklı ilaç yüklü hidrojel formülasyonu hazırlanmıştır. Ayrıca bunlara uygun olarak ilaç yüklü olmayan hidrojel formülasyonları da hazırlanmıştır. MET∙HCl için temsili mide sıvısında (pH:1,2) ilaç ve çapraz bağlayıcı konsantrasyonundan bağımsız olarak düşük salım yüzdeleri elde edilmiştir. Bazik pH değerlerine sahip olan temsili bağırsak sıvısı ve vücut sıvısı ortamlarında (pH: 7,4) ise % kümülatif salım miktarlarının daha yüksek olduğu gözlenmiştir. Salım deneylerine paralel olarak gerçekleştirilen şişme deneylerinin salım profillerini destekler nitelikte olduğu gözlemlenmiştir.  Elde edilen salım yüzdeleri kinetik modellemelere yerleştirildiğinde MET∙HCl için en uygun kinetik modelin Hixon-Crowell (R2: 0,9538) ve Korsmeyer-Peppas (R2: 0,9434) kinetik modelleri olduğu tespit edilmiştir. PİOG∙HCl için salım yüzdeleri incelendiğinde düşük çapraz bağlı jelleşme ortamında düşük ilaç konsantrasyonu içeren hidrojel sisteminin hiçbir salım ortamında salım yapmadığı gözlemlenmiştir. Yüksek çapraz bağlayıcı jelleşme ortamda ise düşük çapraz bağlayıcı jelleşme ortamına göre ilaç konsantrasyonundan bağımsız olarak daha yüksek salım yüzdeleri elde edilmiştir. Hidrojellerin, Poli(akrilik asit) (PAA) bazlı hidrojel formülasyonlarının yapısına uygun olarak en fazla bağırsak onu takiben vücut ve en az mide sıvısında şiştiği gözlemlenmiştir. Elde edilen salım yüzdeleri kinetik modellemelere yerleştirildiğinde PİOG∙HCl'in bağırsak sıvısında serbest bırakılması için en iyi kinetik modelin Hixon-Crowell (R2: 0,9526) ve Korsmeyer-Peppas (R2: 0,9907) kinetik modelleri olduğu gözlemlenmiştir. İlaç yüklü ve ilaç yüklenmemiş jellerin infrared spektrumları karşılaştırıldığında piklerde önemli bir kayma gözlemlenmemesi ve yeni pik oluşmaması çalışılan ilaçlar ile PAA jeli arasında kimyasal etkileşim olmadığını göstermektedir.

Abstract:
Controlled drug release systems are developed to provide a more efficient way of drug delivery than conventional methods. In conventional drug delivery, the drug concentration in the blood rises after each administration and rises above the toxic level, then decreases until the next administration, falling below the minimum effective level. As a result, the drug becomes ineffective. The development of new drug delivery system design is vital importance due to limitations such as narrow therapeutic window, necessity of frequent and repetitive drug use, and undesirable side effects. In addition, in order to develop a new drug, some long-lasting and costly clinical studies on the active substance need to be completed. Considering the time and cost of developing a new drug in the clinical drug research and development process, it is advantageous to make existing drugs applicable to controlled release systems.
Hydrogels synthesized as polymeric drug delivery systems used in controlled drug delivery systems are preferred as an effective method. Hydrogels are three-dimensional, hydrophilic polymeric networks composed of homopolymers, copolymers or macromers that can absorb large amounts of water and biological fluids. They are insoluble due to the presence of chemical or physical cross-links between the components. Hydrogels have three-dimensional network structures composed of polymers that can absorb and retain significant amount of water. Hydrogels have become the most preferred materials for the controlled release of the active substance due to their distinctive features such as their ability to absorb water and their mechanical behavior such as swelling and shrinkage that occur in their structures against various stimuli. Due to the hydrophilic groups in its structure, the cross-linked polymeric network begins to swell with an increase in volume and mass depending on the amount of water added. The cross-linked polymeric network exhibits different swelling properties depending on the amount of hydrophilic groups. The presence of more hydrophilic groups causes more swelling in the network structure. Due to the functional groups in their structures, they respond to environmental stimuli such as pH, temperature, glucose, enzyme, electric and magnetic field by volüme changes. Volume changes in hydrogels occur in response to environmental factors, also called external stimuli, such as pH, temperature, light, electric field, magnetic field, glucose, and enzymes. Hydrogels that are sensitive to environmental factors are known as stimuli-responsive or smart hydrogels. In particular, the changing pH values of the human body fluids have led to the preferance of pH-sensitive hydrogels as drug delivery systems.
When a person eats carbohydrates, the body begins to break them down into their simplest form, which is glucose. This glucose then carried to all body cells by the blood stream. In order to provide energy for the human brain and body from glucose, glucose must pass from the blood to the body cells. The hormone insulin, secreted from the beta cells of the organ called the pancreas, facilitates the entry of glucose in the blood to the muscles or to the stores in the liver. Thus, the sugar level in the blood does not rise. Diabetes mellitus (DM) is a group of chronic disorders that occurs when raised levels of blood glucose ocur because the body cannot produce an yor enough of hormone insülin or cannot effectively use insülin it produces. Type 2 DM (T2DM) is the most common type of diabetes, accounting for more than 90% of all diabetics in the world. The number of drugs is quite high and the treatment program is complex because of the complications of the disease which usually occurs in advanced ages. An effective treatment may not be provided due to problems such as forgetting to take the drugs on time, mixing of drugs, using the wrong dose of drugs or quitting the drug on one's own preference. It is of great importance for treatment to increase the therapeutic efficacy of the drug, to reduce the fluctuations in drug concentration in plasma and the side effects of the drug with controlled drug release systems. Diabetes, which requires constant medical care, leads to multiple organ damage if not well controlled for a long time. In the treatment of T2DM, it is recommended to avoid the use of agents that keep blood sugar at a normal low level (hypoglycemia) and to have a positive or completely neutral effect of drugs in terms of weight, cardiovascular and cerebrovascular.
In this study, metformin and pioglitazone, which is among the antihyperglycemic agents used in the treatment of T2DM, was studied. Metformin, a biguanide derivative, is currently recommended as first-line therapy for all newly diagnosed T2DM patients. The major effect of metformin is to decrease hepatic glucose output as an antihyperglycemic agent. Metformin decreases hepatic glucose production (also called gluconeogenesis), increases insulin-mediated glucose utilization in peripheral tissues (e.g. liver and muscle) and lowers blood glucose levels. Metformin is a relatively safe and well tolerated drug with known pharmacokinetics and manageable toxicities. The oral bioavailability of MET is relatively low (about 50-60%), it is absorbed from the small intestine and reaches its peak plasma concentration in about 2 hours. 
Pioglitazone is also an antihyperglycemic agent. Pioglitazone (PIOG) is an antidiabetic agent of the thiazolidinedione group that reduces insulin resistance in adipose tissue, liver and muscles. It exerts its effect through the activation of a nuclear receptor, PPARγ (peroxisome proliferator activating receptor-γ). The mean absolute bioavailability of pioglitazone 83% and is well absorbed. Although its half-life is 5-6 hours, its glucose-lowering effect may persist for 16-23 hours due to its active metabolites. Thiazolidinediones may cause fluid retention and edema depending on the dose and duration of use. For this reason, it is not recommended to use them together with insulin, especially in patients with heart failure.
In the present study, the antihyperglycemic drugs Metformin Hydrochloride (MET∙HCl) and Pioglitazone Hydrochloride (PİOG∙HCl) used in the treatment of T2DM were examined. For this purpose, pH sensitive poly(acrylic acid) (PAA)-based hydrogels have been prepared by radical polymerization technique. The release studies of prepared hydrogels were investigated in three different conditions mimicking the gastric (pH: 1.2), intestinal (pH: 7.4), and physiological body fluids (pH: 7.4) at 37°C. The cumulative amount of released drug as a percentage was calculated by measuring the absorbance of the liquids taken from these environments at certain time intervals. Degree of swelling of the respective hydrogels and release kinetics were also compered. Four different drug-loaded hydrogel formulations were prepared to compare drug concentration and crosslinker concentration for each active ingredient. In addition, corresponding drug-free hydrogel formulations were also prepared. According to the results obtained, it was observed that less drug release occurred for MET∙HCl, independent of drug and crosslinker concentration, in a representative gastric environment (pH:1,2) with a low pH value. In the representative intestinal and physiological body fluids with basic pH values (pH: 7.4), it was observed that a more effective concentration was released due to ionization. It has been observed that swelling tests performed in parallel with the release experiments support the release profiles. When the results obtained were placed in the kinetic models for MET∙HCl, it was determined that the most suitable models were Hixon-Crowell (R2: 0.9538) and Korsmeyer-Peppas (R2: 0.9344). When the % cumulative release percentages for PIOG∙HCl were examined, it was observed that the hydrogel system containing low drug concentration in the low cross-linked gelling medium did not release in any release medium. When the % cumulative release percentages for PIOG∙HCl were examined, it was observed that the hydrogel system containing low drug concentration in the low cross-linked concentration gelling medium did not release in any release environment. It has been observed that hydrogel systems prepared with a higher amount of crosslinker achieve higher release percentages than hydrogel systems prepared with a lower amount of crosslinker, regardless of drug concentration. PİOG∙HCl's swelling experiment results showed that, in accordance with the nature of PAA-based hydrogel formulations, hydrogels swelled most in intestinal fluid, followed by physiological body fluid and least gastric fluid. When the results obtained were placed in the kinetic models for MET∙HCl, it was determined that the most suitable models were Hixon-Crowell (R2: 0,9526) ve Korsmeyer-Peppas (R2: 0,9907). When the infrared spectra of drug-loaded and drug-free gels are compared, no significant shift in the peaks and the absence of new peaks indicate that there is no chemical interaction between the studied drugs and the PAA gel.