Type 1 diabetes (T1D) is a metabolic disorder characterized by destruction of the pancreatic beta-islet cells leading to complete loss of insulin production. Gliclazide is used in Type 2 diabetes (T2D) to stimulate insulin production but it also has beneficial extrapancreatic effects which make it potentially useful in T1D. In fact, some T2D patients continue to use gliclazide even after their diabetes progresses to T1D since it provides better glycemic control than insulin alone. About 30% of a gliclazide dose undergoes enterohepatic recirculation which may contribute to the observed high interindividual variability in its pharmacokinetics. This may limit its efficacy in T1D especially since diabetes can disturb the gut microbiota and give rise to changes in bile composition and enterohepatic recirculation. Improving the absorption of gliclazide through the use of bile acids and probiotics may reduce this variability and improve the efficacy of gliclazide in T1D. The aim of this thesis was to investigate the interaction between the semisynthetic bile acid, 12-monoketocholic acid (MKC) and gliclazide in terms of pharmacokinetics and hypoglycemic effects in a rat model of T1D with and without probiotic pretreatment. A parallel ex vivo (Ussing chamber) study was carried out to investigate the mechanism of the interaction. Sensitive LC-MS and HPLC methods (Chapter 2) were developed to determine the concentrations of gliclazide and MKC in Ringer's solution and rat serum. Diabetes was induced in male Wistar rats by intravenous (i.v.) alloxan (30 mg/kg). Rats with blood glucose concentration > 18 mmol/l and serum insulin concentration < 0.04 [mu]g/l, 2-3 days after alloxan injection were considered diabetic. A total of 280 male Wistar rats (Chapter 3) were randomly allocated into 28 groups (n=10) of which 14 were made diabetic. Then 7 groups of healthy and 7 groups of diabetic rats were gavaged with probiotics (10⁸ CFU/mg, 75 mg/kg) every 12 hours for three days after which single doses of gliclazide (20 mg/kg), MKC (4 mg/kg) or the combination were administered either by tail vein injection (i.v.) or by gavage. The other 14 groups (7 healthy and 7 diabetic) were gavaged with saline every 12 hours for three days and then treated in the same way. Blood samples were collected from the tail vein for 10 hours after the dose and analyzed for blood glucose, serum gliclazide & serum MKC concentrations. Serum concentration-time curves for gliclazide and MKC were used to determine pharmacokinetic parameters. In the parallel ex vivo study (Chapter 4), 88 rats were randomly divided into 22 groups (n=4 rats per group, 8 chambers per rat), of which 11 groups were made diabetic. Of the 22 groups, 8 groups (4 healthy and 4 diabetic) were pretreated with probiotics as described above to study their influence on gliclazide and MKC flux, 8 groups (4 healthy and 4 diabetic) were used to investigate the interaction between gliclazide and MKC during transport, and 6 groups (3 healthy and 3 diabetic) were used to study the influence of selective inhibitors of the drug transporters Mrp2, Mrp3 and Mdr1 on gliclazide flux. 10 cm piece of the ileum was removed from each rat, the underlying muscle layer and connective tissue removed and the epithelial sheets mounted into Ussing chambers. Gliclazide, MKC or a combination were added to either the mucosal or serosal side and samples collected from both sides for 3 h to determine mucosal-to-serosal absorptive flux (Jss[MtoS]) and serosal-to-mucosal secretory flux (Jss[StoM]) of gliclazide and MKC as appropriate. In diabetic rats, gliclazide alone had no effect on blood glucose levels (Ch3, exp2) whereas MKC reduced it from 23 � 3 to 18 � 3 mmol/l (Ch3, exp3) and the combination of gliclazide and MKC reduced it even further from 24 � 4 to 16 � 3 mmol/l (Ch3, exp4). In diabetic rats, probiotic treatment reduced blood glucose by 2-fold (Ch3, exp1) and enhanced the hypoglycemic effect of the combination of gliclazide and MKC (blood glucose decreased from 24 � 3 to 10 � 2 mmol/l). The bioavailability of gliclazide was higher in healthy rats (53.2 � 6.2%) than in diabetic rats (39.9 � 6.0%) (Ch3, exp2). In healthy rats, MKC enhanced gliclazide bioavailability (82.7 � 8.2%) but in diabetic rats MKC had no effect on gliclazide bioavailability (Ch3, exp4). In healthy rats, probiotic pretreatment significantly reduced gliclazide and MKC bioavailabilities (p<0.01) while in diabetic rats, probiotic pretreatment significantly increased the low bioavailability of gliclazide to a level similar to that in healthy rats (Ch3, exp2 & 3). MKC showed clear evidence of enterohepatic recycling and probiotics delayed and reduced its systemic absorption (Ch3, exp3). In ileal tissues from healthy rats, Ussing chamber studies showed gliclazide is most likely a substrate of Mrp2 and Mrp3 (Ch4, exp5) and MKC significantly reduced gliclazide Jss[MtoS] probably through Mrp3 inhibition (Ch4, exp1). In ileal tissue from diabetic rats, MKC had no effect on gliclazide Jss[MtoS] and Jss[StoM] (Ch4, exp2) and none of the inhibitors had any effect of gliclazide flux (Ch4, exp6). This suggests that these transporters are dysfunctional in this model of T1D. Probiotics and MKC have hypoglycemic effects that appear to be enhanced by gliclazide and all appear to interact at the level of ileal drug transporters. The combination of probiotic treatment, gliclazide and MKC exerted the greatest hypoglycemic effect in T1D rats. Accordingly, the application of this combination may have potential in improving the treatment of T1D.

Type 1 diabetes (T1D) is a metabolic disorder characterized by destruction of the pancreatic beta-islet cells leading to complete loss of insulin production. Gliclazide is used in Type 2 diabetes (T2D) to stimulate insulin production but it also has beneficial extrapancreatic effects which make it potentially useful in T1D. In fact, some T2D patients continue to use gliclazide even after their diabetes progresses to T1D since it provides better glycemic control than insulin alone. About 30% of a gliclazide dose undergoes enterohepatic recirculation which may contribute to the observed high interindividual variability in its pharmacokinetics. This may limit its efficacy in T1D especially since diabetes can disturb the gut microbiota and give rise to changes in bile composition and enterohepatic recirculation. Improving the absorption of gliclazide through the use of bile acids and probiotics may reduce this variability and improve the efficacy of gliclazide in T1D. The aim of this thesis was to investigate the interaction between the semisynthetic bile acid, 12-monoketocholic acid (MKC) and gliclazide in terms of pharmacokinetics and hypoglycemic effects in a rat model of T1D with and without probiotic pretreatment. A parallel ex vivo (Ussing chamber) study was carried out to investigate the mechanism of the interaction. Sensitive LC-MS and HPLC methods (Chapter 2) were developed to determine the concentrations of gliclazide and MKC in Ringer's solution and rat serum. Diabetes was induced in male Wistar rats by intravenous (i.v.) alloxan (30 mg/kg). Rats with blood glucose concentration > 18 mmol/l and serum insulin concentration < 0.04 [mu]g/l, 2-3 days after alloxan injection were considered diabetic. A total of 280 male Wistar rats (Chapter 3) were randomly allocated into 28 groups (n=10) of which 14 were made diabetic. Then 7 groups of healthy and 7 groups of diabetic rats were gavaged with probiotics (10⁸ CFU/mg, 75 mg/kg) every 12 hours for three days after which single doses of gliclazide (20 mg/kg), MKC (4 mg/kg) or the combination were administered either by tail vein injection (i.v.) or by gavage. The other 14 groups (7 healthy and 7 diabetic) were gavaged with saline every 12 hours for three days and then treated in the same way. Blood samples were collected from the tail vein for 10 hours after the dose and analyzed for blood glucose, serum gliclazide & serum MKC concentrations. Serum concentration-time curves for gliclazide and MKC were used to determine pharmacokinetic parameters. In the parallel ex vivo study (Chapter 4), 88 rats were randomly divided into 22 groups (n=4 rats per group, 8 chambers per rat), of which 11 groups were made diabetic. Of the 22 groups, 8 groups (4 healthy and 4 diabetic) were pretreated with probiotics as described above to study their influence on gliclazide and MKC flux, 8 groups (4 healthy and 4 diabetic) were used to investigate the interaction between gliclazide and MKC during transport, and 6 groups (3 healthy and 3 diabetic) were used to study the influence of selective inhibitors of the drug transporters Mrp2, Mrp3 and Mdr1 on gliclazide flux. 10 cm piece of the ileum was removed from each rat, the underlying muscle layer and connective tissue removed and the epithelial sheets mounted into Ussing chambers. Gliclazide, MKC or a combination were added to either the mucosal or serosal side and samples collected from both sides for 3 h to determine mucosal-to-serosal absorptive flux (Jss[MtoS]) and serosal-to-mucosal secretory flux (Jss[StoM]) of gliclazide and MKC as appropriate. In diabetic rats, gliclazide alone had no effect on blood glucose levels (Ch3, exp2) whereas MKC reduced it from 23 � 3 to 18 � 3 mmol/l (Ch3, exp3) and the combination of gliclazide and MKC reduced it even further from 24 � 4 to 16 � 3 mmol/l (Ch3, exp4). In diabetic rats, probiotic treatment reduced blood glucose by 2-fold (Ch3, exp1) and enhanced the hypoglycemic effect of the combination of gliclazide and MKC (blood glucose decreased from 24 � 3 to 10 � 2 mmol/l). The bioavailability of gliclazide was higher in healthy rats (53.2 � 6.2%) than in diabetic rats (39.9 � 6.0%) (Ch3, exp2). In healthy rats, MKC enhanced gliclazide bioavailability (82.7 � 8.2%) but in diabetic rats MKC had no effect on gliclazide bioavailability (Ch3, exp4). In healthy rats, probiotic pretreatment significantly reduced gliclazide and MKC bioavailabilities (p<0.01) while in diabetic rats, probiotic pretreatment significantly increased the low bioavailability of gliclazide to a level similar to that in healthy rats (Ch3, exp2 & 3). MKC showed clear evidence of enterohepatic recycling and probiotics delayed and reduced its systemic absorption (Ch3, exp3). In ileal tissues from healthy rats, Ussing chamber studies showed gliclazide is most likely a substrate of Mrp2 and Mrp3 (Ch4, exp5) and MKC significantly reduced gliclazide Jss[MtoS] probably through Mrp3 inhibition (Ch4, exp1). In ileal tissue from diabetic rats, MKC had no effect on gliclazide Jss[MtoS] and Jss[StoM] (Ch4, exp2) and none of the inhibitors had any effect of gliclazide flux (Ch4, exp6). This suggests that these transporters are dysfunctional in this model of T1D. Probiotics and MKC have hypoglycemic effects that appear to be enhanced by gliclazide and all appear to interact at the level of ileal drug transporters. The combination of probiotic treatment, gliclazide and MKC exerted the greatest hypoglycemic effect in T1D rats. Accordingly, the application of this combination may have potential in improving the treatment of T1D.

Submitted by Rosivalda Pereira (mrs.pereira@ufma.br) on 2017-05-08T20:15:35Z No. of bitstreams: 1 FranciscaSilva.pdf: 4464543 bytes, checksum: 4e3dc826f1a161f6f567a3489b8e9fb4 (MD5) / Made available in DSpace on 2017-05-08T20:15:35Z (GMT). No. of bitstreams: 1 FranciscaSilva.pdf: 4464543 bytes, checksum: 4e3dc826f1a161f6f567a3489b8e9fb4 (MD5) Previous issue date: 2016-11-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa e ao Desenvolvimento Científico e Tecnológico do Maranhão (FAPEMA) / Gliclazide (GLZ) is an oral antidiabetic agent used for glycemic control in patients with Diabetes Mellitus Type II (DMII). The GLZ has high membrane permeability and low aqueous solubility, contributing to the reduction of its therapeutic effectiveness. The cocrystals drug synthesis is a form of increasing its water solubility and its bioavailability. This work aimed to synthesize and characterize a novel co-crystal of GLZ using as coformer tromethamine (TRIS). Therefore, it was carried out the computational study using the Gauss 09W software, aiming to study the structural conformation energy of GLZ and TRIS molecules for the investigation of possible interactions between API and coformer. Subsequently, the synthesis of co-crystal GLZ-TRIS (1:1) was performed by liquid-assisted manual grinding and liquid-assisted ball mill grinding process. Subsequently, the co-crystal was characterized by the Powder X-ray diffraction method (PXRD), Fourier Transform Infrared Spectroscopy (FT-IR), Raman Spectroscopy Thermogravimetry and Differential Thermal Analysis Simultaneous (TG-DTA), Differential Scanning Calorimetry (DSC) and fotovisual DSC. Moreover, the stoichiometric ratio of co-crystal was obtained from the construction of the binary phase diagrams using the DSC technique. The computational study showed the major potential energy sites for GLZ and TRIS, serving as a basis for the prediction of possible groups of molecular interaction between the molecules under study. The results obtained by XRPD showed the formation of a new crystalline phase (co-crystal) for the binary mixture of GLZ with TRIS. The binary phase diagram showed the formation of the co-crystal GLZ-TRIS in the molar ratio 1:1. The FTIR and Raman analysis of this co-crystal indicated significant changes in their vibrational modes from which is possible to infer the main sites of interaction by hydrogen bonds involved in the formation of this material. The results of the thermoanalytical study obtained by TG-DTA and DSC showed that the co-crystal presented different thermal properties as compared to the starting compounds, exhibiting intermediate stability to these last compounds. The TG-DTA indicated that the co-crystal has stability until at 150.0 °C. In DSC study, the co-crystal presented a melting point at 144.0 °C, which was confirmed by analysis of fotovisual DSC. In addition, the cyclic DSC showed a crystallization cycle transition in the second heating cycle. Thus, it is concluded that both methods of cocrystallization used in this study yielded in the synthesis of new cocrystal GLZ-TRIS (1:1). These methods presented more advantageous over other methods of cocrystallization, because they require less time of synthesis and less amount of solvent. Therefore, the co-crystal synthesized in this work is presented as a very promising and new pharmaceutical solid form of GLZ for the production of safer and more effective drugs in DMII therapy. / A gliclazida (GLZ) é um antidiabético oral utilizado para o controle da glicemia em pacientes portadores do Diabetes Mellitus Tipo II (DMII). A GLZ possui elevada permeabilidade membranar e baixa solubilidade aquosa, contribuindo para a redução da sua eficácia terapêutica. A síntese de cocristais de fármacos constitui uma forma de aumentar a sua hidrossolubilidade e a sua biodisponibilidade. Assim, este trabalho objetivou sintetizar e caracterizar um novo cocristal de GLZ, utilizando como coformador a trometamina (TRIS). Para tanto, foi realizado o estudo computacional utilizando o software Gauss 09W, visando estudar a conformação estrutural de energia das moléculas de GLZ e TRIS para a investigação das possíveis interações entre o fármaco e o coformador. Posteriormente, a síntese do cocristal de GLZ-TRIS na razão molar de 1:1, foi realizada por moagem líquido-assistida manual e por moagem líquido-assistida via moinho de bolas. Em seguida, o cocristal foi caracterizado por Difração de Raios X pelo método do pó (DRXP), Espectroscopia no Infravermelho com Transformada de Fourier (FTIR), Espectroscopia Raman, Termogravimetria e Análise Térmica Diferencial Simultâneas (TG-DTA), Calorimetria Exploratória Diferencial (DSC) e DSC fotovisual. Além disso, a relação estequiométrica do cocristal foi obtida a partir da construção do diagrama de fases binário, utilizando a técnica de DSC. O estudo computacional mostrou os principais sítios de energia potencial para a GLZ e a TRIS, servindo como base para a predição dos possíveis grupos moleculares de interação entre as moléculas em estudo. Os resultados obtidos por DRXP mostraram a formação de uma nova fase cristalina (cocristal) para a mistura binária de GLZ com a TRIS. O diagrama de fases binário apresentou evidências da formação do cocristal de GLZ-TRIS na razão molar de 1:1. As análises de FTIR e Raman deste cocristal indicaram alterações significativas nos seus modos vibracionais, sendo possível inferir os principais sítios de interação por ligações de hidrogênio envolvidas na formação deste material. Os resultados do estudo termoanalítico obtidos por TG-DTA e por DSC mostraram que o cocristal apresentou propriedades térmicas diferentes dos seus compostos de partida, exibindo estabilidade intermediária a estes compostos. O TG-DTA indicou que o cocristal possui estabilidade até 150°C. No estudo por DSC o cocristal apresentou um ponto de fusão em 144°C, sendo confirmado pela análise de DSC fotovisual. Além disso, o DSC cíclico indicou uma transição de cristalização no segundo ciclo de aquecimento. Assim, conclui-se que ambas as metodologias de cocristalização utilizadas neste estudo resultaram na síntese de um novo cocristal de GLZ-TRIS (1:1). Estas metodologias apresentam-se mais vantajosas em relação a outras metodologias de cocristalização, pois elas requerem menor tempo de síntese e menor quantidade de solvente. Portanto, o cocristal sintetizado neste trabalho apresenta-se como uma nova forma sólida farmacêutica de GLZ muito promissora para a produção de medicamentos mais seguros e eficazes na terapia do DMII.

<p>Gliklazid je jedan od najče&scaron;će kori&scaron;ćenih lekova u terapiji dijabetes melitusa tip 2. U poslednje vreme, utvrđeno je da gliklazid ispoljava i druge pozitivne farmakolo&scaron;ke efekte kao &scaron;to su imunomodulatorni i anti-koagulacioni efekti, ukazujući na njegovu potencijalnu primenu u terapiji dijabetes melitusa tip 1. Gliklazid se odlikuje varijabilnim stepenom apsorpcije nakon peroralne primene i iz tog razloga pretpostavlja se da bi tehnike njegove ciljane isporuke, kao &scaron;to je mikroinkapsulacija, mogle da dovedu do pobolj&scaron;anja njegove apsorpcije i njegove potencijalne primene u terapiji T1DM. Pokazano je da različite žučne kiseline, uključujući i holnu, imaju stabilizacione efekte u domenu primene mikrovezikula i kontrolisanog osobađanja lekova, te je moguće da bi njihov dodatak u mikrovezikularnu formulaciju gliklazida mogao dodatno da pobolj&scaron;a oslobađanje gliklazida, njegovu apsorpciju i antidijabetičke efekte. S tim u vezi, cilj ovog istraživanja je da se ispita hipoglikemijski efekat gliklazida primenjenog u obliku alginatnih mikrovezikula, sa ili bez dodatka holne kiseline na T1DM modelu pacova. Trideset &scaron;est pacova obolelih od T1DM indukovanog aloksanom i odgovarajuće zdrave kontrolne životinje su nasumično raspoređene u &scaron;est grupa (n=6) i tretirane jednokratnom dozom fiziolo&scaron;kog rastvora, suspenzijom gliklazida, gliklazidom u obliku alginatnih mikrovezikula, samo holnom kiselinom, i mikrovezikulama gliklazida sa ili baz dodatka holne kiseline. Uzorkovana je krv tokom 10 h nakon unete doze i merena je koncentracija glukoze u krvi I koncentracija gliklazida u serumu kori&scaron;ćenjem HPLC metode. Mikrovezikule gliklazida su ispoljile hipo-glikemijski efekat kod pacova obolelih od dijabetesa, uprkos njegovim smanjenim koncentracijama u serumu, dok je dodatak holne kiseline u mikrovezikularnu formulaciju smanjio hipoglikemijski efekat gliklazida. Ovo potvrđuje izostanak sinergističkog efekta između gliklazida i holne kiseline. Takođe, ni proces mikroinkapsulacije niti dodatak holne kiseline nisu doprineli pobolj&scaron;anju apsorpcije gliklazida, &scaron;to ukazuje na činjenicu da su njegovi hipoglikemijski efekti nezavisni od njegove apsorpcije i koncentracije u serumu. Stoga se može pretpostaviti da su hipoglikemijski efekti gliklazida pre pod uticajem crevno-metaboličke aktivacije nego ciljanog oslobađanja u digestivnom traktu sistemske apsorpcije. Mikrovezikule gliklazida ispoljavaju hipoglikemijski efekat kod pacova obolelih od T1DM nezavisno od insulina, te mogu imati potencijalnu primenu u terapiji T1DM. Ovaj rad su podržali: HORIZON 2020 MEDLEM projekat broj 690876; Projekat Sekretarijata naučnog i tehnolo&scaron;kog razvoja Vojvodine broj . 114-451-2072-/2016-02; Projekat Ministarstva obrazovanja, nauke i tehnolo&scaron;kog razvoja Republike Srbije broja 41012.</p> / <p><!--[if gte mso 9]><xml> <o:DocumentProperties> <o:Author>mladen</o:Author> <o:Version>16.00</o:Version> </o:DocumentProperties> <o:OfficeDocumentSettings> <o:AllowPNG/> </o:OfficeDocumentSettings></xml><![endif]--><!--[if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <w:TrackMoves/> <w:TrackFormatting/> <w:PunctuationKerning/> <w:ValidateAgainstSchemas/> <w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid> <w:IgnoreMixedContent>false</w:IgnoreMixedContent> <w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText> <w:DoNotPromoteQF/> <w:LidThemeOther>EN-US</w:LidThemeOther> <w:LidThemeAsian>X-NONE</w:LidThemeAsian> <w:LidThemeComplexScript>X-NONE</w:LidThemeComplexScript> 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Major depression is a highly prevalent mood disorder with chronic debilitating effects. Additional to a rising rate in incidence, depression is highly co–morbid with other psychiatric disorders, but also chronic cardiometabolic illnesses that present with an inflammatory component. The exact aetiology of depression is still unknown, being multifactorial in its possible aetiology. Various hypotheses have attempted to shed light on both endogenous and exogenous risk factors as well as the underlying pathology that may lead to the development of the disease. This has led to a wide range of mediators being implicated, including biogenic amines, the HPA–axis, neurotrophic factors, inflammatory agents, the cholinergic system and circadian rhythm, to name a few. The mechanisms of action of current treatment strategies, except for a few atypical and novel treatment approaches, are limited to interactions with monoamines and are at best only 65% effective. Many of these are also plagued by troubling side–effects, relapse and recurrence. It has therefore become imperative to explore novel targets for the treatment of depression that may produce more rapid, robust and lasting antidepressant effects with a less daunting side–effect profile. The strong co–morbidity between depression and various cardiometabolic disorders, including cardiovascular disease, atherosclerosis, type 2 diabetes mellitus (T2DM) and metabolic syndrome (MetS) has led to the proposal that a metabolic disturbance may be a vital component that drives inflammatory and immunological dysfunction in depression. Supporting of this is evidence for a role of inflammatory cytokines and neurotrophic factors in the pathogenesis of depression. It has also been demonstrated that a link exists between insulin– and nitric oxide (NO)– mediated pathways in the brain, which further highlights the role of oxidative stress and cell damage. Furthermore, evidence supports a role for oxidative stress and NO in T2DM and/or insulin resistance. Insulin has also been implicated in various physiological processes in the central nervous system (CNS) and may also influence the release and reuptake of neurotransmitters. Preclinical and clinical evidence has provided support for the antidepressant–like effects of insulin–sensitizing peroxisome proliferator activated receptor (PPAR)– agonists, such as rosiglitazone and pioglitazone. In preclinical studies, however, these effects are limited to acute treatment with pioglitazone or sub–chronic (5 days) treatment with rosiglitazone. It is well–recognized that such findings need to be confirmed by chronic treatment paradigms. The aim of the current study was therefore to further investigate the proposed antidepressant–like effects of pioglitazone in a genetic animal model of depression, the Flinders sensitive line (FSL) rat, using a chronic treatment protocol. The FSL rat model was reaffirmed as presenting with inherent depressive–like behaviour compared to its more resilient counterpart, the Flinders resistant line (FRL) rat. Moreover, imipramine demonstrated a robust and reliable antidepressant–like effect in these animals using the forced swim test (FST), thus confirming the face and predictive validity of the FSL rat model for depression. In contrast to previous preclinical studies, acute dose–ranging studies with pioglitazone in Sprague Dawley rats delivered no significant anti–immobility effects in the FST, whereas results similar to that seen in the dose–ranging studies were observed following chronic treatment using FSL rats. Since altered pharmacokinetics could possibly influence the drug’s performance, another route of administration, viz. the subcutaneous route, was utilized as an additional measure to exclude this possibility. The results of the subcutaneous study, however, were congruent with that observed after oral treatment. In order to confirm an association between altered insulin sensitivity and antidepressant action and demonstration by recent studies that thiazolidinediones may augment the efficacy of existing antidepressants, we therefore investigated whether concomitant treatment with gliclazide (an insulin releaser and insulin desensitizer) or pioglitazone (an insulin sensitizer) may alter the antidepressant–like effects evoked by chronic treatment with imipramine. Pioglitazone did not positively or negatively affect the antidepressant effect of imipramine, although gliclazide tended to decrease the anti–immobility effects induced by this antidepressant. Taken together and considering the current available literature, this finding supports evidence linking the insulin–PPAR pathway to depression. However, further explorative studies are required to delineate the role of insulin sensitivity and glucose homeostasis in depression and antidepressant response. / Thesis (M.Sc. (Pharmacology))--North-West University, Potchefstroom Campus, 2012.

Major depression is a highly prevalent mood disorder with chronic debilitating effects. Additional to a rising rate in incidence, depression is highly co–morbid with other psychiatric disorders, but also chronic cardiometabolic illnesses that present with an inflammatory component. The exact aetiology of depression is still unknown, being multifactorial in its possible aetiology. Various hypotheses have attempted to shed light on both endogenous and exogenous risk factors as well as the underlying pathology that may lead to the development of the disease. This has led to a wide range of mediators being implicated, including biogenic amines, the HPA–axis, neurotrophic factors, inflammatory agents, the cholinergic system and circadian rhythm, to name a few. The mechanisms of action of current treatment strategies, except for a few atypical and novel treatment approaches, are limited to interactions with monoamines and are at best only 65% effective. Many of these are also plagued by troubling side–effects, relapse and recurrence. It has therefore become imperative to explore novel targets for the treatment of depression that may produce more rapid, robust and lasting antidepressant effects with a less daunting side–effect profile. The strong co–morbidity between depression and various cardiometabolic disorders, including cardiovascular disease, atherosclerosis, type 2 diabetes mellitus (T2DM) and metabolic syndrome (MetS) has led to the proposal that a metabolic disturbance may be a vital component that drives inflammatory and immunological dysfunction in depression. Supporting of this is evidence for a role of inflammatory cytokines and neurotrophic factors in the pathogenesis of depression. It has also been demonstrated that a link exists between insulin– and nitric oxide (NO)– mediated pathways in the brain, which further highlights the role of oxidative stress and cell damage. Furthermore, evidence supports a role for oxidative stress and NO in T2DM and/or insulin resistance. Insulin has also been implicated in various physiological processes in the central nervous system (CNS) and may also influence the release and reuptake of neurotransmitters. Preclinical and clinical evidence has provided support for the antidepressant–like effects of insulin–sensitizing peroxisome proliferator activated receptor (PPAR)– agonists, such as rosiglitazone and pioglitazone. In preclinical studies, however, these effects are limited to acute treatment with pioglitazone or sub–chronic (5 days) treatment with rosiglitazone. It is well–recognized that such findings need to be confirmed by chronic treatment paradigms. The aim of the current study was therefore to further investigate the proposed antidepressant–like effects of pioglitazone in a genetic animal model of depression, the Flinders sensitive line (FSL) rat, using a chronic treatment protocol. The FSL rat model was reaffirmed as presenting with inherent depressive–like behaviour compared to its more resilient counterpart, the Flinders resistant line (FRL) rat. Moreover, imipramine demonstrated a robust and reliable antidepressant–like effect in these animals using the forced swim test (FST), thus confirming the face and predictive validity of the FSL rat model for depression. In contrast to previous preclinical studies, acute dose–ranging studies with pioglitazone in Sprague Dawley rats delivered no significant anti–immobility effects in the FST, whereas results similar to that seen in the dose–ranging studies were observed following chronic treatment using FSL rats. Since altered pharmacokinetics could possibly influence the drug’s performance, another route of administration, viz. the subcutaneous route, was utilized as an additional measure to exclude this possibility. The results of the subcutaneous study, however, were congruent with that observed after oral treatment. In order to confirm an association between altered insulin sensitivity and antidepressant action and demonstration by recent studies that thiazolidinediones may augment the efficacy of existing antidepressants, we therefore investigated whether concomitant treatment with gliclazide (an insulin releaser and insulin desensitizer) or pioglitazone (an insulin sensitizer) may alter the antidepressant–like effects evoked by chronic treatment with imipramine. Pioglitazone did not positively or negatively affect the antidepressant effect of imipramine, although gliclazide tended to decrease the anti–immobility effects induced by this antidepressant. Taken together and considering the current available literature, this finding supports evidence linking the insulin–PPAR pathway to depression. However, further explorative studies are required to delineate the role of insulin sensitivity and glucose homeostasis in depression and antidepressant response. / Thesis (M.Sc. (Pharmacology))--North-West University, Potchefstroom Campus, 2012.