Redefining the role of thiazolidinediones in the management of type 2 diabetes

Peroxisome proliferator-activated receptors as targets to treat metabolic diseases: Focus on the adipose tissue, liver, and pancreas

The world is experiencing reflections of the intersection of two pandemics: Obesity and coronavirus disease 2019. The prevalence of obesity has tripled since 1975 worldwide, representing substantial public health costs due to its comorbidities. The adipose tissue is the initial site of obesity impairments. During excessive energy intake, it undergoes hyperplasia and hypertrophy until overt inflammation and insulin resistance turn adipocytes into dysfunctional cells that send lipotoxic signals to other organs. The pancreas is one of the organs most affected by obesity. Once lipotoxicity becomes chronic, there is an increase in insulin secretion by pancreatic beta cells, a surrogate for type 2 diabetes mellitus (T2DM). These alterations threaten the survival of the pancreatic islets, which tend to become dysfunctional, reaching exhaustion in the long term. As for the liver, lipotoxicity favors lipogenesis and impairs beta-oxidation, resulting in hepatic steatosis. This silent disease affects around 30% of the worldwide population and can evolve into end-stage liver disease. Although therapy for hepatic steatosis remains to be defined, peroxisome proliferator-activated receptors (PPARs) activation copes with T2DM management. Peroxisome PPARs are transcription factors found at the intersection of several metabolic pathways, leading to insulin resistance relief, improved thermogenesis, and expressive hepatic steatosis mitigation by increasing mitochondrial beta-oxidation. This review aimed to update the potential of PPAR agonists as targets to treat metabolic diseases, focusing on adipose tissue plasticity and hepatic and pancreatic remodeling.

The Impact of Exercise on Immunity, Metabolism, and Atherosclerosis

Physical exercise represents an effective preventive and therapeutic strategy beneficially modifying the course of multiple diseases. The protective mechanisms of exercise are manifold; primarily, they are elicited by alterations in metabolic and inflammatory pathways. Exercise intensity and duration strongly influence the provoked response. This narrative review aims to provide comprehensive up-to-date insights into the beneficial effects of physical exercise by illustrating the impact of moderate and vigorous exercise on innate and adaptive immunity. Specifically, we describe qualitative and quantitative changes in different leukocyte subsets while distinguishing between acute and chronic exercise effects. Further, we elaborate on how exercise modifies the progression of atherosclerosis, the leading cause of death worldwide, representing a prime example of a disease triggered by metabolic and inflammatory pathways. Here, we describe how exercise counteracts causal contributors and thereby improves outcomes. In addition, we identify gaps that still need to be addressed in the future.

Therapeutic potentials of agonist and antagonist of adenosine receptors in type 2 diabetes

Type 2 diabetes has been a global health challenge over the decades and is among the leading causes of death. Several treatment approaches have been developed, but more effective and new therapies are still needed. The role of adenosine in glucose and lipid homeostasis has offered a different therapeutic approach. Adenosine mediates its physiological role through the activation of adenosine receptors. These adenosine receptors have been implicated in glucose and lipid homeostasis. The ability of agonists and antagonists of adenosine receptors to activate or inhibit the adenosine signalling cascade and thereby affecting the balance of glucose and lipid homeostasis has challenged the studies of agonists and antagonists of adenosine receptors, both preclinical and clinical, as potential anti-diabetic drugs. This review provides a background on different anti-diabetic therapeutic approaches, outlining the role of adenosine receptors in glucose and lipid homeostasis, and mechanisms underlying the action of agonists/antagonists of adenosine receptors as a therapeutic potential towards type 2 diabetes.

Combination therapies with thiazolidinediones are associated with a lower risk of acute exacerbations in new-onset COPD patients with advanced diabetic mellitus: a cohort-based case-control study

BACKGROUND

The effects of oral antihyperglycaemic drugs (OADs) for type 2 diabetes mellitus (T2DM) on the outcomes of co-existing chronic obstructive pulmonary disease (COPD) patients are not well studied. We examined the association of combinational OADs and the risk of acute exacerbations of COPD (AECOPD) in T2DM patients with co-existing COPD.

METHODS

A cohort-based case-control study was conducted using data from the National Health Insurance Research Database of Taiwan. Among new-onset COPD-T2DM patients, 65,370 were prescribed metformin and 2nd-line OADs before the date of COPD onset. Each AECOPD case was matched to 4 randomly selected controls according to the propensity score estimated by the patient's baseline characteristics. Conditional logistic regression analysis was performed to estimate the association between AECOPD risk and OAD use.

RESULTS

Among COPD-T2DM patients, 3355 AECOPD cases and 13,420 matched controls were selected. Of the patients treated with a double combination of oral OADs (n = 12,916), those treated with sulfonylurea (SU) and thiazolidinediones (TZD) had a lower AECOPD risk than the patients who received metformin (MET) and SU, with an adjusted odds ratio (OR) of 0.69 (95% confidence interval [CI] 0.51-0.94, P = 0.02). Of the patients with a triple combination of oral OADs (n = 3859), we found that those treated with MET, SU and TZD had a lower risk of AECOPD (adjusted OR 0.81 (0.68-0.96, P = 0.01) than a combination of MET, SU and α-glucosidase inhibitors (AGIs) regardless of the level of COPD complexity.

CONCLUSION

Combination therapies with TZD were associated with a reduced risk of AECOPD in advanced T2DM patients with co-existing COPD.

SGLT2 inhibitor ipragliflozin alone and combined with pioglitazone prevents progression of nonalcoholic steatohepatitis in a type 2 diabetes rodent model

Nonalcoholic steatohepatitis (NASH) has become the most common cause of chronic liver disease worldwide in recent years. The pathogenesis of NASH is closely linked to metabolic diseases such as insulin resistance, obesity, dyslipidemia, and type 2 diabetes. However, there is currently no pharmacological agent for preventing the progression of NASH. Sodium-glucose cotransporter (SGLT) 2 inhibitors increase urinary glucose excretion by inhibiting renal glucose reabsorption, and improve various pathological conditions of type 2 diabetes, including insulin resistance. In the present study, we examined the effects of ipragliflozin, a SGLT2-selective inhibitor, alone and in combination with pioglitazone on NASH in high-fat diet-fed KK/A^y type 2 diabetic mice. Type 2 diabetic mice with NASH exhibited steatosis, inflammation, and fibrosis in the liver as well as hyperglycemia, insulin resistance, and obesity, features that are observed in human NASH. Four-week repeated administration of ipragliflozin (0.1-3 mg/kg) led to significant improvements in hyperglycemia, insulin resistance, and obesity in addition to hyperlipidemia and liver injury including hepatic steatosis and fibrosis. Moreover, ipragliflozin reduced inflammation and oxidative stress in the liver. Repeated administration of pioglitazone (3-30 mg/kg) also significantly improved various parameters of diabetes and NASH, excluding obesity. Furthermore, combined treatment comprising ipragliflozin (1 mg/kg) and pioglitazone (10 mg/kg) additively improved these parameters. These findings indicate that the SGLT2-selective inhibitor ipragliflozin improves hyperglycemia as well as NASH in type 2 diabetic mice. Therefore, treatment with ipragliflozin monotherapy or coadministered with pioglitazone is expected to be a potential therapeutic option for the treatment of type 2 diabetes with NASH.

Rosiglitazone has a neutral effect on the risk of dementia in type 2 diabetes patients

This study investigated whether rosiglitazone might increase or reduce dementia risk. Taiwan’s National Health Insurance database was used to enroll a cohort of 1:1 matched-pairs of ever and never users of rosiglitazone based on propensity score from patients with new-onset type 2 diabetes during 1999-2006. The patients were alive on January 1, 2007 and were followed up for dementia until December 31, 2011. A total of 5,048 pairs of never users and ever users were identified. The incident case numbers were 127 and 121, respectively. The adjusted hazard ratio for ever versus never users was 0.895 (95% confidence interval: 0.696-1.151). The adjusted hazard ratios for the first (<12.1 months), second (12.1-25.1 months) and third (>25.1 months) tertiles of cumulative duration of rosiglitazone therapy were 0.756 (0.509-1.123), 0.964 (0.685-1.357) and 0.949 (0.671-1.341), respectively. When cumulative duration was treated as a continuous variable, the adjusted hazard ratio was 1.000 (0.992-1.008). Subgroup analyses conducted in ever users and never users of metformin and in patients diagnosed with diabetes during three different periods of time, i.e., 1999-2000, 2001-2003 and 2004-2006, all supported a neutral effect of rosiglitazone. In conclusion, rosiglitazone does not increase or redcue the risk of dementia.

Sixty Years of Drug Discovery for Type 2 Diabetes: Where Are We Now?

Today, excluding insulin, there are eight classes of anti-diabetic medicines that have been added to the pharmacy since the introduction of metformin in the mid-1950s; the sulfonylureas, biguanides, thiazolidinediones, α-glucosidase inhibitors, meglitinides, incretins, and sodium glucose transport 2 inhibitors. Does the fact that metformin is still first-line treatment suggest that our drug discovery efforts over the past 60 years have not been good enough? Or does it suggest that diabetes is such a complex disorder that no single treatment, other than gastric bypass surgery, can affect true normalization of not only blood sugar but also the underlying pathologies? Our understanding of the disease has most definitely improved which may bring hope for the future in terms of science, but for it to be beneficial, this science has to be translated into better drug treatments for the disease. In this review, I have examined the eight classes of anti-diabetes drugs from a drug discovery perspective.

PPARs: regulators of metabolism and as therapeutic targets in cardiovascular disease. Part I: PPAR-α

This article provides a comprehensive review about the molecular and metabolic actions of PPAR-α. It describes its structural features, ligand specificity, gene transcription mechanisms, functional characteristics and target genes. In addition, recent progress with the use of loss of function and gain of function mouse models in the discovery of diverse biological functions of PPAR-α, particularly in the vascular system and the status of the development of new single, dual, pan and partial PPAR agonists (PPAR modulators) in the clinical management of metabolic diseases are presented. This review also summarizes the clinical outcomes from a large number of clinical trials aimed at evaluating the atheroprotective actions of current clinically used PPAR-α agonists, fibrates and statin-fibrate combination therapy.

Practical combination therapy based on pathophysiology of type 2 diabetes

Type 2 diabetes is a complex, chronic, and progressive condition that often necessitates the use of multiple medications to achieve glycemic goals. Clinical guidelines generally recommend intensifying pharmacotherapy if glycemic goals are not achieved after 3 months of treatment. However, for many patients with type 2 diabetes, treatment intensification is delayed or does not occur. Initiating combination therapy early in the disease course has the potential to delay disease progression and improve patient outcomes. Guidelines generally provide a list of agents that may be used in combination regimens and emphasize individualization of treatment. The purpose of this review is to discuss the rationale for combination therapy, considering treatment effects on pathophysiologic aspects of type 2 diabetes and individual drug profiles. The combination of newer antidiabetes therapies with complementary mechanisms of action provides the opportunity to target multiple sites of tissue, organ, and cellular dysfunction.

Efficacy, safety and impact on β-cell function of dipeptidyl peptidase-4 inhibitors plus metformin combination therapy in patients with type 2 diabetes and the difference between Asians and Caucasians: a meta-analysis

BACKGROUND

To assess the efficacy, safety and impact on β-cell function of DPP-4 inhibitors plus metformin in T2DM patients and their difference between Asians and Caucasians.

METHODS

We conducted a literature search (from 1 January 2000 to 14 April 2015) for RCTs of DPP-4 inhibitors plus metformin combination therapy in T2DM.

RESULTS

A total of 27 RCTs were included. Compared with metformin, DPP-4 inhibitor plus metformin therapy was associated with higher reduction in HbA1c [-0.61 %, -0.69 to -0.52], FPG [-1.10 mmol/l, -1.29 to -0.92], TC [-0.11 mmol/l, -0.20 to -0.02], TG [-0.21 mmol/l, -0.33 to -0.10], HOMA-IR [-0.19, -0.36 to -0.02], gastrointestinal adverse events [OR 0.86, 0.77-0.97] and higher increment in HOMA-β [10.21, 7.73-12.69]. Comparison of HbA1c, FPG, body weight and HOMA-IR changes between Asian and Caucasian patients did not show a significant between-group difference of -0.05 % (-0.30, 0.20; P = 0.69), 0.17 mmol/l (-0.52, 0.85; P = 0.62), -0.15 kg (-0.64, 0.35; P = 0.53) and 0.27 (-0.98, 1.53; P = 0.64) compared with metformin. Comparisons of HOMA-β between Asian and Caucasian patients showed a significant between-group difference of -7.68 (-14.95, -0.42; P = 0.04).

CONCLUSION

DPP-4 inhibitors and metformin therapy was effective and safe for T2DM patients. The glucose-lowering efficacy of DPP-4 inhibitors was same in Asian and Caucasian patients, although the effect on HOMA-β was inferior in Asian patients. The effect of DPP-4 inhibitors on HOMA-IR and body weight in Asian patients was comparable with that observed in Caucasian patients.

Peroxisome Proliferator-Activated Receptors and the Heart: Lessons from the Past and Future Directions

Peroxisome proliferator-activated receptors (PPARs) belong to the nuclear family of ligand activated transcriptional factors and comprise three different isoforms, PPAR-α, PPAR-β/δ, and PPAR-γ. The main role of PPARs is to regulate the expression of genes involved in lipid and glucose metabolism. Several studies have demonstrated that PPAR agonists improve dyslipidemia and glucose control in animals, supporting their potential as a promising therapeutic option to treat diabetes and dyslipidemia. However, substantial differences exist in the therapeutic or adverse effects of specific drug candidates, and clinical studies have yielded inconsistent data on their cardioprotective effects. This review summarizes the current knowledge regarding the molecular function of PPARs and the mechanisms of the PPAR regulation by posttranslational modification in the heart. We also describe the results and lessons learned from important clinical trials on PPAR agonists and discuss the potential future directions for this class of drugs.

Role of Nitric Oxide Synthase Uncoupling at Rostral Ventrolateral Medulla in Redox-Sensitive Hypertension Associated With Metabolic Syndrome

Metabolic syndrome (MetS), which is rapidly becoming prevalent worldwide, is long known to be associated with hypertension and recently with oxidative stress. Of note is that oxidative stress in the rostral ventrolateral medulla (RVLM), where sympathetic premotor neurons reside, contributes to sympathoexcitation and hypertension. This study sought to identify the source of tissue oxidative stress in RVLM and their roles in neural mechanism of hypertension associated with MetS. Adult normotensive rats subjected to a high-fructose diet for 8 weeks developed metabolic traits of MetS, alongside increases in sympathetic vasomotor activity and blood pressure. In RVLM of these MetS rats, the tissue level of reactive oxygen species was increased, nitric oxide (NO) was decreased, and mitochondrial electron transport capacity was reduced. Whereas the protein expression of neuronal NO synthase (nNOS) or protein inhibitor of nNOS was increased, the ratio of nNOS dimer/monomer was significantly decreased. Oral intake of pioglitazone or intracisternal infusion of tempol or coenzyme Q 10 significantly abrogated all those molecular events in high-fructose diet–fed rats and ameliorated sympathoexcitation and hypertension. Gene silencing of protein inhibitor of nNOS mRNA in RVLM using lentivirus carrying small hairpin RNA inhibited protein inhibitor of nNOS expression, increased the ratio of nNOS dimer/monomer, restored NO content, and alleviated oxidative stress in RVLM of high-fructose diet–fed rats, alongside significantly reduced sympathoexcitation and hypertension. These results suggest that redox-sensitive and protein inhibitor of nNOS–mediated nNOS uncoupling is engaged in a vicious cycle that sustains the production of reactive oxygen species in RVLM, resulting in sympathoexcitation and hypertension associated with MetS.

Peroxisome proliferator-activated receptors for hypertension

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors belonging to the nuclear receptor superfamily, which is composed of four members encoded by distinct genes (α, β, γ, and δ). The genes undergo transactivation or transrepression under specific mechanisms that lead to the induction or repression of target gene expression. As is the case with other nuclear receptors, all four PPAR isoforms contain five or six structural regions in four functional domains; namely, A/B, C, D, and E/F. PPARs have many functions, particularly functions involving control of vascular tone, inflammation, and energy homeostasis, and are, therefore, important targets for hypertension, obesity, obesity-induced inflammation, and metabolic syndrome in general. Hence, PPARs also represent drug targets, and PPARα and PPARγ agonists are used clinically in the treatment of dyslipidemia and type 2 diabetes mellitus, respectively. Because of their pleiotropic effects, they have been identified as active in a number of diseases and are targets for the development of a broad range of therapies for a variety of diseases. It is likely that the range of PPARγ agonist therapeutic actions will result in novel approaches to lifestyle and other diseases. The combination of PPARs with reagents or with other cardiovascular drugs, such as diuretics and angiotensin II receptor blockers, should be studied. This article provides a review of PPAR isoform characteristics, a discussion of progress in our understanding of the biological actions of PPARs, and a summary of PPAR agonist development for patient management. We also include a summary of the experimental and clinical evidence obtained from animal studies and clinical trials conducted to evaluate the usefulness and effectiveness of PPAR agonists in the treatment of lifestyle-related diseases.

Pioglitazone does not affect the risk of kidney cancer in patients with type 2 diabetes

OBJECTIVE

To investigate whether pioglitazone treatment of patients with type 2 diabetes mellitus was associated with an increased risk of kidney cancer.

METHODS

The reimbursement databases of all Taiwanese patients with type 2 diabetes who received oral anti-diabetic agents or insulin from 1996 to 2009 were retrieved from the National Health Insurance. An entry date was set at 1 January 2006, and a total of 1,093,675 patients with type 2 diabetes were followed up for kidney cancer incidence until the end of 2009. The incidences of kidney cancer among patients who had and had not received pioglitazone, as well as among subgroups of those treated with pioglitazone (sorted by time since starting pioglitazone, duration of treatment and cumulative dose) were calculated and hazard ratios (HRs) estimated by Cox regression analysis.

RESULTS

Of the 1,093,675 patients, 58,172 (5.3%) had and 1,035,503 (94.7%) had not received pioglitazone, with incident kidney cancer developing in 208 (0.36%) and 3304 (0.32%) patients, respectively, and a respective incidence of 97.7 and 90.5 per 100,000 person-years. Pioglitazone and kidney cancer were not significantly associated in unadjusted (HR 1.04; 95% confidence interval (CI), 0.90-1.20), age-sex-adjusted (HR 1.09; 95% CI, 0.95-1.25), and fully adjusted (HR 1.09; 95% CI, 0.94-1.26) models. None of the dose-response parameters showed a significant trend of risk association, with all P-trends >0.10.

CONCLUSIONS

Pioglitazone does not affect the risk of kidney cancer.

[Cardiovascular effects and safety of glucose-lowering drugs: current situation]

Diabetes mellitus is an independent cardiovascular risk factor. Therefore, in addition to normalising blood glucose, the aim of the treatment for diabetes mellitus should be to prevent cardiovascular complications. However, the evidence available on the cardio-protective role of the different glucose-lowering drugs is scarce and poor, particularly as regards with the risk of major cardiovascular events. In this context, the regulatory agencies have modified the regulations for the approval of glucose-lowering drugs, now requiring to demonstrate the glucose-lowering effect together with a robust assessment of the cardiovascular safety. The aim of this work is to review the cardiovascular effects of the different glucose-lowering drugs, focusing on their impact on the risk of major cardiovascular events.

Efficacy and safety of dipeptidyl peptidase-4 inhibitors and metformin as initial combination therapy and as monotherapy in patients with type 2 diabetes mellitus: a meta-analysis

AIMS

This meta-analysis was performed to provide an update on the efficacy and safety of dipeptidyl peptidase-4 (DPP-4) inhibitors and metformin as initial combination therapy and as monotherapy in patients with type 2 diabetes mellitus (T2DM).

METHODS

We conducted a search on MEDLINE, Embase and Cochrane Collaborative database for randomized controlled trials (RCTs) of DPP-4 inhibitors and metformin as initial combination therapy or as monotherapy in patients with T2DM by the end of December 2012, using the key words 'alogliptin', 'dutogliptin', 'linagliptin', 'saxagliptin', 'sitagliptin', 'vildagliptin' and 'metformin'. RCTs were selected for meta-analysis if (1) they were RCTs comparing DPP-4 inhibitors plus metformin as initial combination therapy or DPP-4 inhibitor monotherapy to metformin monotherapy, (2) duration of treatment was ≥12 weeks and (3) reported data on haemoglobin A1c (HbA1c) change, fasting plasma glucose (FPG) change, weight change, adverse cardiovascular (CV) events, hypoglycaemia or gastrointestinal adverse events (AEs).

RESULTS

A total of eight RCTs were included. Compared with metformin monotherapy, DPP-4 inhibitors monotherapy was associated with lower reduction in HbA1c level [weighted mean differences (MD) = 0.28, 95% confidence intervals (CIs) (0.17, 0.40), p < 0.00001], lower reduction in FPG level [MD = 0.81, 95% CI(0.60, 1.02), p <0.00001], lower weight loss [MD = 1.51, 95% CI (0.89, 2.13), p < 0.00001], but lower risk of adverse CV events [risk ratio (RR) = 0.36, 95% CI (0.15, 0.85), p = 0.02], lower risk of hypoglycaemia [RR = 0.44, 95% CI (0.27, 0.72), p = 0.001] and lower risk of gastrointestinal AEs [RR = 0.63, 95% CI(0.55, 0.70), p <0.00001]. Compared with metformin monotherapy, DPP-4 inhibitors plus metformin as initial combination therapy was associated with higher reduction in HbA1c level [MD = -0.49, 95% CI (-0.57, -0.40), p < 0.00001], higher reduction in FPG level [MD = -0.80, 95% CI (-0.87, -0.74), p < 0.00001], lower weight loss [MD = 0.44, 95% CI (0.22, 0.67), p = 0.0001]; but was not associated with a further reduction in adverse CV events [RR=0.54, 95% CI (0.25, 1.19), p = 0.13], nor the higher risk of hypoglycaemia [RR = 1.04, 95% CI (0.72, 1.50), p = 0.82], nor the prolonged risk of gastrointestinal AEs [RR = 0.98, 95% CI (0.88, 1.10), p = 0.77].

CONCLUSIONS

DPP-4 inhibitors, which are safe and effective in controlling the blood glucose, may possibly decrease the risk of CV events in patients with T2DM. It could be a credible alternative for T2DM patients who, for some reason, cannot use metformin, or are in high risk of CV exposure. High-quality, large sample and long-term follow-up clinical trails are needed to confirm the long-term conclusions.

Clinical utility in the treatment of type 2 diabetes with the saxagliptin/metformin fixed combination

Fixed-dose combination (FDC) products represent a widely accepted approach to type 2 diabetes treatment, given that monotherapies sometimes fail to meet the treatment targets - obtaining a sustained reduction in micro- and macrovascular complications. Saxagliptin (SAXA)/metformin (MET) FDC tablets can be used either alone or in combination with glyburide, thiazolidinediones, or insulin. It has been proven that the SAXA/MET combination leads to a significant improvement in glycemic control compared to placebo in patients with type 2 diabetes that is inadequately controlled with MET alone. In addition, this FDC has been proven to be safe for people with diabetes mellitus and established cardiovascular disease, elderly patients, and patients with impaired renal function (>30 mL/minute), with dosage modification. Patient compliance, adherence, and persistence to the therapeutic regimen has been shown to be very good, while the titration of each compound according to the patient's profile is easy, given the availability of different formulations. The SAXA/MET FDC is a patient-friendly, dosage-flexible, and hypoglycemia-safe regimen with very few adverse events and a neutral or even favorable effect on body weight. It achieves significant glycosylated hemoglobin A1c reduction helping the patient to achieve his/her individual glycemic goals.

Do thiazolidinediones still have a role in treatment of type 2 diabetes mellitus?

Thiazolidinediones have been introduced in the treatment of type 2 diabetes mellitus (T2DM) since the late 1990s. Although troglitazone was withdrawn from the market a few years later due to liver toxicity, both rosiglitazone and pioglitazone gained widespread use for T2DM treatment. In 2010, however, due to increased risk of cardiovascular events associated with its use, the European Medicines Agency recommended suspension of rosiglitazone use and the Food and Drug Administration severely restricted its use. Thus pioglitazone is the only thiazolidinedione still significantly employed for treating T2DM and it is the only molecule of this class still listed in the American Diabetes Association-European Association for the Study of Diabetes 2012 Position Statement. However, as for the other thiazolidinediones, use of pioglitazone is itself limited by several side effects, some of them potentially dangerous. This, together with the development of novel therapeutic strategies approved in the last couple of years, has made it questionable whether or not thiazolidinediones (namely pioglitazone) should still be used in the treatment of T2DM. This article will attempt to formulate an answer to this question by critically reviewing the available data on the numerous advantages and the potentially worrying shortcomings of pioglitazone treatment in T2DM.

Differential sensitivities of the vascular K(ATP) channel to various PPAR activators

Several agonists of the peroxisome proliferator-activated receptors (PPARs) are currently used for the treatment of metabolic disorders including diabetes. We have recently shown that one of them, Rosiglitazone, inhibits the vascular ATP-sensitive K⁺ (K(ATP)) channel and compromises the coronary vasodilation by the β-adrenoceptor agonist. Here, we show evidence for the channel inhibition by various PPAR agonists, information that may be useful for finding new therapeutical agents with less cardiovascular side-effects and more selective K(ATP) channel blockers targeting at the K(ir)6.1 subunit. Structural comparison of these PPAR agonists may shed insight into the critical chemical groups for the channel inhibition. K(ir)6.1/SUR2B channel was expressed in HEK293 cells and studied in whole-cell voltage clamp. The K(ir)6.1/SUR2B channel was strongly inhibited by several PPAR(γ) agonists with potencies similar to, or higher than, that of Rosiglitazone, while other PPAR(γ) agonists barely inhibited the channel. The K(ir)6.1/SUR2B channel was also inhibited by PPAR(α) and PPAR(β/δ) agonists with intermediate potencies. The structure necessary for the channel inhibition appears to include the thiazole linked to an aromatic or furan ring. Additions of side groups such as small aliphatic chain increased the potency for channel inhibition, while additions of aromatic rings reduced it. These results indicate that the PPAR(γ) agonists with weak K(ATP) channel inhibition may be potential candidates as therapeutical agents, and those with strong channel inhibition may be used as selective K(ATP) channel blockers. The structural information of the PPAR agonists may be useful for the development of new therapeutical modalities with less cardiovascular side-effects.

Rosiglitazone selectively inhibits K(ATP) channels by acting on the K(IR) 6 subunit

BACKGROUND AND PURPOSE

Rosiglitazone is an anti-diabetic drug acting as an insulin sensitizer. We recently found that rosiglitazone also inhibits the vascular isoform of ATP-sensitive K(+) channels and compromises vasodilatory effects of β-adrenoceptor activation and pinacidil. As its potency for the channel inhibition is in the micromolar range, rosiglitazone may be used as an effective K(ATP) channel inhibitor for research and therapeutic purposes. Therefore, we performed experiments to determine whether other isoforms of K(ATP) channels are also sensitive to rosiglitazone and what their sensitivities are.

EXPERIMENTAL APPROACH

K(IR) 6.1/SUR2B, K(IR) 6.2/SUR1, K(IR) 6.2/SUR2A, K(IR) 6.2/SUR2B and K(IR) 6.2ΔC36 channels were expressed in HEK293 cells and were studied using patch-clamp techniques.

KEY RESULTS

Rosiglitazone inhibited all isoforms of K(ATP) channels in excised patches and in the whole-cell configuration. Its IC(50) was 10 µmol·L(-1) for the K(IR) 6.1/SUR2B channel and ∼45 µmol·L(-1) for K(IR) 6.2/SURx channels. Rosiglitazone also inhibited K(IR) 6.2ΔC36 channels in the absence of the sulphonylurea receptor (SUR) subunit, with potency (IC(50) = 45 µmol·L(-1) ) almost identical to that for K(IR) 6.2/SURx channels. Single-channel kinetic analysis showed that the channel inhibition was mediated by augmentation of the long-lasting closures without affecting the channel open state and unitary conductance. In contrast, rosiglitazone had no effect on K(IR) 1.1, K(IR) 2.1 and K(IR) 4.1 channels, suggesting that the channel inhibitory effect is selective for K(IR) 6.x channels.

CONCLUSIONS AND IMPLICATIONS

These results suggest a novel K(ATP) channel inhibitor that acts on the pore-forming K(IR) 6.x subunit, affecting the channel gating.

Outcomes and lessons from the PROactive study

Beyond improvement of glucose control, thiazolidinediones exert pleiotropic effects, which may contribute to some cardiovascular protection. PROactive ("PROspective pioglitAzone Clinical Trial In macroVascular Events") has provided valuable, although controversial, information on the impact of pioglitazone on cardiovascular outcomes in a high-risk population of patients with type 2 diabetes and established macrovascular disease. Since 2005, there has been much debate on the relative value of the statistically non-significant 10% reduction in the quite challenging primary composite endpoint (combining cardiovascular disease-driven and procedural events in all vascular beds) versus the statistically significant 16% decrease in the more robust and conventional main secondary endpoint (all-cause mortality, myocardial infarction, and stroke) observed with pioglitazone. Revisiting PROactive deserves much interest following the report of inconclusive results on cardiovascular efficacy and safety of rosiglitazone in RECORD, the withdrawal (limitation) of rosiglitazone because of cardiovascular safety concern, the recent publication of a statement positioning pioglitazone in type 2 diabetes and the near availability of cheaper generics of pioglitazone. Although subanalyses may have more limited value from a statistical viewpoint, they nonetheless can provide valuable information on the drug efficacy/safety profile and clinical insights into which patients might benefit most (in terms of cardiovascular outcomes) from pioglitazone therapy.

Dipeptidyl peptidase-4 inhibitors: 3 years of experience

According to the latest American Diabetes Association guidelines, lowering glycated hemoglobin (HbA(1c)) to below or around 7% has been shown to reduce microvascular and neuropathic complications of diabetes and, if implemented soon after the diagnosis of diabetes, is associated with long-term reduction in macrovascular disease. Recently a new class of antidiabetes drugs has been developed, dipeptidyl peptidase-4 (DPP-4) inhibitors, which act by inhibiting DPP-4, the enzyme that inactivates glucagon-like peptide-1 (GLP-1). Through the inhibition of DPP-4, DPP-4 inhibitors enhance the effects of GLP-1 and glucose-dependent insulinotropic peptide, increasing glucose-mediated insulin secretion and suppressing glucagon secretion. We conducted a review analyzing clinical efficacy and safety of DPP-4 inhibitors, both alone and in combination with other antidiabetes drugs, including randomized controlled trials about sitagliptin, vildagliptin, saxagliptin, and linagliptin conducted in the latest 15 years. We concluded that, once metformin fails to maintain glycemic control, addition of DPP-4 inhibitors should be the logical choice: they seems to lower HbA(1c) levels by 0.6-0.9 percentage points and to have a comparable effect on HbA(1c) versus the addition of a sulfonylurea or glitazone. They also have positive effects on β-cell function, and they have neutral effects on body weight. Furthermore, DPP-4 inhibitors prevent the risk of hypoglycemia posed by sulfonylureas.

Beneficial effects of pioglitazone against cardiovascular injury are enhanced by combination with aliskiren in a rat model of diabetic nephropathy

OBJECTIVES

Aliskiren is the first in a new class of orally active direct renin inhibitors, approved for the treatment of hypertension. However, the efficacy of aliskiren in diabetic cardiovascular complications remains to be defined. This study aimed to test the hypothesis that aliskiren may enhance the beneficial effects of pioglitazone against cardiovascular injury associated with diabetic nephropathy.

METHODS

Diabetic nephropathy was induced in rats by unilateral nephrectomy followed by streptozotocin injection. Diabetic nephropathic rats were orally given vehicle, pioglitazone, aliskiren, or combined pioglitazone and aliskiren for four weeks to compare their effects on cardiovascular injury, particularly myocardial fibrosis.

KEY FINDINGS

Pioglitazone treatment significantly attenuated cardiac lipid peroxidation, oxidative injury and myocardial fibrosis in diabetic nephropathic rats. This was associated with up-regulation of transforming growth factor-β1 and matrix metalloproteinase-2 genes, along with down-regulation of tissue inhibitor of metalloproteinase-2 gene in cardiac tissue. The combination of aliskiren with pioglitazone exerted greater beneficial effect than monotherapy with either drug, on all the aforementioned parameters.

CONCLUSIONS

Our findings suggested that aliskiren enhanced the protective effects of pioglitazone against myocardial fibrosis, in experimental diabetic nephropathy. Thus, the combination of aliskiren and pioglitazone may be a potential therapeutic strategy for cardiovascular injury associated with diabetic nephropathy.

Pioglitazone is a valid alternative to rosiglitazone

In 2000, two new thiazolidinediones, pioglitazone and rosiglitazone, were approved for the treatment of type 2 diabetes mellitus (T2DM). Administered as monotherapy or in combination with other antihyperglycemic agents, they represented an effective option for achieving or maintaining good glycemic control in patients with T2DM. Despite their efficacy, there was increasing concern regarding the potential of an increased cardiovascular risk with rosiglitazone. This resulted in the suspension of rosiglitazone from the European market by the European Medicines Agency in September 2010. This article focuses on the various steps that led to this important decision, and discusses a possible alternative for the treatment of patients receiving rosiglitazone.

Rosiglitazone inhibits vascular KATP channels and coronary vasodilation produced by isoprenaline

BACKGROUND AND PURPOSE

Rosiglitazone is an anti-diabetic drug improving insulin sensitivity and glucose uptake in skeletal muscle and adipose tissues. However, several recent clinical trials suggest that rosiglitazone can increase the risk of cardiovascular ischaemia, although other studies failed to show such risks. Therefore, the effects of rosiglitazone on the coronary circulation and any potential vascular targets need to be elucidated. Here, we show that the vascular isoform of the ATP-sensitive K(+) (K(ATP) ) channel is inhibited by rosiglitazone, impairing physiological regulation of the coronary circulation.

EXPERIMENTAL APPROACH

The K(IR) 6.1/SUR2B channel was expressed in HEK293 cells and studied in whole-cell and inside-out patch configurations. The Langendorff heart preparation was used to evaluate rosiglitazone in the coronary circulation of wild-type (WT) and K(IR) 6.1-null (Kcnj8(-/-) ) mice.

KEY RESULTS

K(IR) 6.1/SUR2B channels in HEK cells were inhibited by rosiglitazone in a membrane-delimited manner. This effect was markedly enhanced by sub-micromolar concentrations of glibenclamide and the IC(50) for rosiglitazone fell to 2µM, a therapeutically achievable concentration. In the Langendorff heart preparation rosiglitazone inhibited, concentration-dependently, the coronary vasodilation induced by isoprenaline, without affecting basal coronary tone. Effects of rosiglitazone on coronary perfusion were attenuated by more than 50% in the Kcnj8(-/-) mice, supporting the involvement of K(ATP) channels in this effect of rosiglitazone on the coronary circulation.

CONCLUSIONS AND IMPLICATIONS

These results indicate that the vascular K(ATP) channel is one of the targets of rosiglitazone action, through which this drug may compromise coronary responses to circulating vasodilators and perhaps also to metabolic stress.

Management of type 2 diabetes: new and future developments in treatment

The increasing prevalence, variable pathogenesis, progressive natural history, and complications of type 2 diabetes emphasise the urgent need for new treatment strategies. Longacting (eg, once weekly) agonists of the glucagon-like-peptide-1 receptor are advanced in development, and they improve prandial insulin secretion, reduce excess glucagon production, and promote satiety. Trials of inhibitors of dipeptidyl peptidase 4, which enhance the effect of endogenous incretin hormones, are also nearing completion. Novel approaches to glycaemic regulation include use of inhibitors of the sodium-glucose cotransporter 2, which increase renal glucose elimination, and inhibitors of 11β-hydroxysteroid dehydrogenase 1, which reduce the glucocorticoid effects in liver and fat. Insulin-releasing glucokinase activators and pancreatic-G-protein-coupled fatty-acid-receptor agonists, glucagon-receptor antagonists, and metabolic inhibitors of hepatic glucose output are being assessed. Early proof of principle has been shown for compounds that enhance and partly mimic insulin action and replicate some effects of bariatric surgery.

Initial combination therapy with saxagliptin and metformin provides sustained glycaemic control and is well tolerated for up to 76 weeks

AIM

To assess the efficacy and safety of saxagliptin + metformin initial combination therapy compared with saxagliptin or metformin alone over 76 weeks (24-week short-term + 52-week long-term extension) in treatment-naÏve type 2 diabetes mellitus patients with inadequate glycaemic control.

METHODS

In this phase 3, parallel-group, double-blind, active-controlled study, 1306 patients 18-77 years of age (HbA1c 8.0-12.0%) were randomized to saxagliptin 5 mg + 500 mg metformin, saxagliptin 10 mg + 500 mg metformin, saxagliptin 10 mg + placebo or 500 mg metformin + placebo. Blinded metformin was titrated during weeks 1-5 of the short-term treatment period in 500 mg/day increments to 2000 mg/day maximum in the metformin-based treatment groups. No titration of metformin was permitted during the long-term treatment period. A total of 888 patients completed the study (76 weeks), 613 without being rescued. Changes in HbA1c, fasting plasma glucose, 120-min postprandial glucose (PPG) and PPG-area under the curve (AUC) from baseline to week 76 were analysed using a repeated-measures model.

RESULTS

At 76 weeks, adjusted mean changes from baseline HbA1c (95% CI) for saxagliptin 5 mg + metformin, saxagliptin 10 mg + metformin, saxagliptin 10 mg and metformin were -2.31 (-2.44, -2.18), -2.33 (-2.46, -2.20), -1.55 (-1.70, -1.40) and -1.79% (-1.93, -1.65), respectively (post hoc and nominal p < 0.0001 vs. metformin and saxagliptin monotherapies for saxagliptin 5 mg + metformin and saxagliptin 10 mg + metformin). The proportions of patients requiring rescue or discontinuation for insufficient glycaemic control were lower for saxagliptin + metformin than for either monotherapy. Little or no attenuation in PPG-AUC or 120-min PPG was observed between weeks 24 and 76 for saxagliptin + metformin, indicating persistent efficacy. Adverse event rates were similar across groups; hypoglycaemic events occurred at a low frequency.

CONCLUSION

Saxagliptin + metformin initial combination therapy was well tolerated and produced sustained glycaemic control for up to 76 weeks, with greater improvements in glycaemic parameters compared with either drug alone.

Safety and efficacy of saxagliptin added to thiazolidinedione over 76 weeks in patients with type 2 diabetes mellitus

To assess the long-term efficacy and safety of saxagliptin in patients with type 2 diabetes mellitus inadequately controlled with thiazolidinedione monotherapy, 565 patients were randomised to saxagliptin (2.5 mg or 5 mg) or placebo added to thiazolidinedione over 76 weeks (24-week short-term + 52-week long-term extension period) in this phase 3, double-blind, placebo-controlled trial; 360 patients completed the study. At 76 weeks, adjusted mean changes from baseline HbA(1C) (repeated measures model; 95% CI) for saxagliptin 2.5 mg, 5 mg, and placebo were -0.59% (-0.75, -0.43), -1.09% (-1.26, -0.93), and -0.20% (-0.39, -0.01), respectively (post hoc and nominal p=0.0019 and p<0.0001 for saxagliptin 2.5 mg and 5 mg vs. placebo, respectively). Adverse event frequency was similar between groups. Confirmed hypoglycaemic events were 1.0% and 0% vs. 0.5% for saxagliptin 2.5 mg and 5 mg vs. placebo, respectively. Results should be interpreted with caution given the proportion of patients who discontinued or required glycaemic rescue therapy during the 76-week course of study. Saxagliptin added to thiazolidinedione provided sustained incremental efficacy vs. placebo with little hypoglycaemia for up to 76 weeks and was generally well tolerated.

Do PPAR-Gamma Agonists Have a Future in Parkinson's Disease Therapy?

Thiazolidinediones (TZDs) are peroxisome proliferator-activated receptor (PPAR)-γ agonists commonly used as insulin-sensitizing drugs for the treatment of type 2 diabetes. In the last decade, PPAR-γ agonists have received increasing attention for their neuroprotective properties displayed in a variety of neurodegenerative diseases, including Parkinson's disease (PD), likely related to the anti-infammatory activity of these compounds. Recent studies indicate that neuroinflammation, specifically reactive microglia, plays important roles in PD pathogenesis. Moreover, after the discovery of infiltrating activated Limphocytes in the substantia nigra (SN) of PD patients, most recent research supports a role of immune-mediated mechanisms in the pathological process leading to chronic neuroinflammation and dopaminergic degeneration. PPAR-γ are highly expressed in cells of both central and peripheral immune systems, playing a pivotal role in microglial activation as well as in monocytes and T cells differentiation, in which they act as key regulators of immune responses. Here, we review preclinical evidences of PPAR-γ-induced neuroprotection in experimental PD models and highlight relative anti-inflammatory mechanisms involving either central or peripheral immunomodulatory activity. Specific targeting of immune functions contributing to neuroinflammation either directly (central) or indirectly (peripheral) may represent a novel therapeutic approach for disease modifying therapies in PD.

Patient considerations and clinical utility of a fixed dose combination of saxagliptin/metformin in the treatment of type 2 diabetes

INTRODUCTION

Targeting glycated hemoglobin (HbA(1c)) levels below 7.0% is considered a primary goal of diabetes care, given its importance in obtaining a sustained reduction in microvascular, and possibly macrovascular complications.

AIM

The aim of this review was to evaluate the clinical utility of a fixed dose combination of saxagliptin/metformin in the treatment of type 2 diabetes.

EVIDENCE REVIEW

The combination of saxagliptin/metformin was well tolerated and produced sustained glycemic control for up to 76 weeks, with greater improvements in glycemic parameters compared with either drug alone. The saxagliptin/metformin combination also proved its non-inferiority compared with either sulfonylurea/metformin or sitagliptin/metformin combinations.

PLACE IN THERAPY

Clinical practice recommends lifestyle interventions together with starting metformin at the time that the type 2 diabetes mellitus is diagnosed. Once metformin fails to maintain glycemic control, the addition of DPP-4 inhibitors should be the logical choice because of their effects on HbA(1c) compared to the addition of a sulfonylurea or glitazone, and because of their positive effects on beta cell function and their neutral effects on body weight. Furthermore, DPP-4 inhibitors prevent the risk of hypoglycemia posed by sulfonylureas.

Targeting type 2 diabetes

The evolving concept of how nutrient excess and inflammation modulate metabolism provides new opportunities for strategies to correct the detrimental health consequences of obesity. In this review, we focus on the complex interplay among lipid overload, immune response, proinflammatory pathways and organelle dysfunction through which excess adiposity might lead to type 2 diabetes. We then consider evidence linking dysregulated CNS circuits to insulin resistance and results on nutrient-sensing pathways emerging from studies with calorie restriction. Subsequently, recent recommendations for the management of type 2 diabetes are discussed with emphasis on prevailing current therapeutic classes of biguanides, thiazolidinediones and incretin-based approaches.

Pioglitazone: beyond glucose control

Pioglitazone is an oral antidiabetic agent that decreases insulin resistance in adipose tissue, liver and muscles. This action is mediated by its link to a nuclear receptor called peroxisome proliferator-activated receptor-gamma. By improving insulin sensitivity, hepatic glucose production decreases and glucose uptake increases in the peripheral tissues. Beyond these effects on glucose metabolism, pioglitazone has positive effects on lipid metabolism, blood pressure, endothelial function, adiponectin and C-reactive protein levels. These make pioglitazone treatment effective beyond glucose control. In this article, current evidence concerning pioglitazone in the treatment of Type 2 diabetes will be reviewed.

Discovery and development of selective PPAR gamma modulators as safe and effective antidiabetic agents

IMPORTANCE OF THE FIELD

PPARgamma full agonists (pioglitazone and rosiglitazone) are the mainstay drugs for the treatment of type 2 diabetes; however, mechanism-based side effects have limited their full therapeutic potential. In recent years, much progress has been achieved in the discovery and development of selective PPARgamma modulators (SPPARgammaMs) as safer alternatives to PPARgamma full agonists.

AREAS COVERED IN THIS REVIEW

This review focuses on the preclinical and clinical data of all the SPPARgammaMs discovered so far, retrieved by searching PubMed, Prous Integrity database and company news updates from 1999 to date.

WHAT THE READER WILL GAIN

Here we thoroughly discuss SPPARgammaMs' mode of action, briefly examine new ways to identify superior SPPARgammaMs, and finally, compare and contrast the pharmacological and safety profile of various agents.

TAKE HOME MESSAGE

The preclinical and clinical findings clearly suggest that selective PPARgamma modulators have the potential to become the next generation of PPARgamma agonists: effective insulin sensitizers with a superior safety profile to that of PPARgamma full agonists.

Administration of thiazolidinediones for neuroprotection in ischemic stroke: a pre-clinical systematic review

Thiazolidinediones (TZDs) may prevent or attenuate CNS injury arising from an ischemic event. We performed meta-analysis of experimental studies in which a TZD (either rosiglitazone or pioglitazone) was administered in a rodent model of focal or global cerebral ischemia. Infarct volume was the primary endpoint for analysis of drug efficacy, and neurological outcome was also assessed. We identified 31 studies through the use of PubMed and Embase, 22 of which met our pre-specified inclusion criteria and were analyzed with the Cochrane Review Manager software. Treatment with TZDs decreased infarct volume and improved neurological outcome regardless of study quality, dose timing, or ischemia model (transient or permanent). Rosiglitazone and pioglitazone were similarly effective in reducing infarct volume and protecting neurologic function. Importantly, the collective data suggest that pre-treatment with a TZD is not required for neuroprotection, although additional studies are clearly needed to define the breadth of the therapeutic window. The data warrant further studies into the potential acute use of TZDs for ischemic stroke therapy in the general population.

Peroxisome proliferator-activated receptors, metabolic syndrome and cardiovascular disease

Metabolic syndrome (MetS) is a constellation of risk factors including insulin resistance, central obesity, dyslipidemia and hypertension that markedly increase the risk of Type 2 diabetes (T2DM) and cardiovascular disease (CVD). The peroxisome proliferators-activated receptor (PPAR) isotypes, PPARα, PPARδ/ß and PPARγ are ligand-activated nuclear transcription factors, which modulate the expression of an array of genes that play a central role in regulating glucose, lipid and cholesterol metabolism, where imbalance can lead to obesity, T2DM and CVD. They are also drug targets, and currently, PPARα (fibrates) and PPARγ (thiazolodinediones) agonists are in clinical use for treating dyslipidemia and T2DM, respectively. These metabolic characteristics of the PPARs, coupled with their involvement in metabolic diseases, mean extensive efforts are underway worldwide to develop new and efficacious PPAR-based therapies for the treatment of additional maladies associated with the MetS. This article presents an overview of the functional characteristics of three PPAR isotypes, discusses recent advances in our understanding of the diverse biological actions of PPARs, particularly in the vascular system, and summarizes the developmental status of new single, dual, pan (multiple) and partial PPAR agonists for the clinical management of key components of MetS, T2DM and CVD. It also summarizes the clinical outcomes from various clinical trials aimed at evaluating the atheroprotective actions of currently used fibrates and thiazolodinediones.

Follow-up of phase I trial of adalimumab and rosiglitazone in FSGS: III. Report of the FONT study group

BACKGROUND

Patients with resistant primary focal segmental glomerulosclerosis (FSGS) are at high risk of progression to chronic kidney disease stage V. Antifibrotic agents may slow or halt this process. We present outcomes of follow-up after a Phase I trial of adalimumab and rosiglitazone, antifibrotic drugs tested in the Novel Therapies in Resistant FSGS (FONT) study.

METHODS

21 patients--12 males and 9 females, age 16.0 +/- 7.5 yr, and estimated GFR (GFRe) 121 +/- 56 mL/min/1.73 m2--received adalimumab (n = 10), 24 mg/m2 every 14 days or rosiglitazone (n = 11), 3 mg/m2 per day for 16 weeks. The change in GFRe per month prior to entry and after completion of the Phase I trial was compared.

RESULTS

19 patients completed the 16-week FONT treatment phase. The observation period pre-FONT was 18.3 +/- 10.2 months and 16.1 +/- 5.7 months after the study. A similar percentage of patients, 71% and 56%, in the rosiglitazone and adalimumab cohorts, respectively, had stabilization in GFRe, defined as a reduced negative slope of the line plotting GFRe versus time without requiring renal replacement therapy after completion of the FONT treatment period (P = 0.63).

CONCLUSION

Nearly 50% of patients with resistant FSGS who receive novel antifibrotic agents may have a legacy effect with delayed deterioration in kidney function after completion of therapy. Based on this proof-of-concept preliminary study, we recommend long-term follow-up of patients enrolled in clinical trials to ascertain a more comprehensive assessment of the efficacy of experimental treatments.

Combination of nateglinide with thiazolidinediones in Type 2 diabetes

Insulin sensitivity and insulin secretion are reciprocally related such that insulin resistance is adapted by increased insulin secretion to maintain normal glucose and lipid homeostasis. Treatment of Type 2 diabetes should aim to restore and sustain the normal relationship between insulin sensitivity and secretion. Nateglinide is a rapid-onset, short-acting insulin-secretion enhancer that restores early-phase insulin secretion, reduces postprandial glucose excursions and prevents long-term hyperinsulinemia. Given its mechanism of action, it is evident that nateglinide would be more effective when used in combination with an insulin sensitizer, such as the thiazolidinediones. Thiazolidinediones do not stimulate insulin release and, therefore, are potentially suitable candidates for combination therapy with an insulin-secretion enhancer, such as nateglinide. Combination therapy of thiazolidinediones with nateglinide is effective, carries low risk of hypoglycemia and is suitable for patients with moderate renal impairment, although weight gain and edema are common side effects. Further studies are needed to determine whether nateglinide in combination with thiazolidinediones will help clinicians better achieve their treatment goals in targeting Type 2 diabetes. Moreover, comparative studies between nateglinide and medications targeting postprandial glycemia, such as dipeptidyl peptidase-4 inhibitors and glucagon-like peptide-1 analogues, are necessary. This article summarizes data concerning the mechanism of action, efficacy and safety of therapy with nateglinide and thiazolidinediones as monotherapy and in combination treatment, and aims at a better understanding of the substrate defects their synergy hopes to defy.