The dipeptidyl peptidase-4 inhibitor linagliptin exhibits time- and dose-dependent localization in kidney, liver, and intestine after intravenous dosing: results from high resolution autoradiography in rats

Elucidation of DPP-4 involvement in systemic distribution and renal reabsorption of linagliptin by PBPK modeling with a cluster Gauss-Newton method

The dipeptidyl peptidase-4 (DPP-4) inhibitor linagliptin (LNG) exhibits target-mediated drug disposition (TMDD) in clinical settings, characterized by saturable binding to plasma soluble DPP-4 (sDPP-4) and tissue transmembrane DPP-4 (tDPP-4). Previous studies have indicated that saturable renal reabsorption of LNG contributes to its nonlinear urinary excretion observed in humans and wild-type mice, but not in Dpp-4 knockout mice. To elucidate the mechanisms underlying these complex phenomena, including DPP-4-related renal reabsorption of LNG, we employed physiologically-based pharmacokinetic (PBPK) modeling combined with a cluster Gauss-Newton method (CGNM). The CGNM facilitated the exploration of parameters in rat and human PBPK models for LNG and the determination of parameter identifiability. Through PBPK-CGNM analysis using reported autoradiography data ([14C]-LNG) in wild-type and Dpp-4-deficient rats, DPP-4-specific distributions of LNG in various tissues were clearly differentiated from nonspecific parts. By fitting to human plasma concentrations and urinary and fecal excretions of LNG after intravenous and oral administrations, multiple unknown PBPK parameters were simultaneously estimated by the CGNM. Notably, the amount of tDPP-4 and the reabsorption clearance for LNG-DPP-4 complexes were identifiable, indicating their critical role in explaining the complex nonlinear pharmacokinetics of LNG. Compared with previous PBPK analyses, the CGNM allowed us to incorporate greater model complexity (e.g., consideration of tDPP-4 expressions and in vitro binding kinetics), ultimately resulting in a more accurate reproduction of LNG's TMDD. In conclusion, by considering LNG as a high-affinity probe for DPP-4, comprehensive PBPK-CGNM analyses suggested a dynamic whole-body distribution of DPP-4, including its involvement in the renal reabsorption of LNG.

Known Drugs Identified by Structure-Based Virtual Screening Are Able to Bind Sigma-1 Receptor and Increase Growth of Huntington Disease Patient-Derived Cells

Huntington disease (HD) is a devastating and presently untreatable neurodegenerative disease characterized by progressively disabling motor and mental manifestations. The sigma-1 receptor (σ1R) is a protein expressed in the central nervous system, whose 3D structure has been recently determined by X-ray crystallography and whose agonists have been shown to have neuroprotective activity in neurodegenerative diseases. To identify therapeutic agents against HD, we have implemented a drug repositioning strategy consisting of: (i) Prediction of the ability of the FDA-approved drugs publicly available through the ZINC database to interact with σ1R by virtual screening, followed by computational docking and visual examination of the 20 highest scoring drugs; and (ii) Assessment of the ability of the six drugs selected by computational analyses to directly bind purified σ1R in vitro by Surface Plasmon Resonance and improve the growth of fibroblasts obtained from HD patients, which is significantly impaired with respect to control cells. All six of the selected drugs proved able to directly bind purified σ1R in vitro and improve the growth of HD cells from both or one HD patient. These results support the validity of the drug repositioning procedure implemented herein for the identification of new therapeutic tools against HD.

Immunohistochemical Pharmacokinetics of the Anti-diabetes Drug Alogliptin in Rat Kidney and Liver

Alogliptin is one of a new class of therapeutic agents for type 2 diabetes called dipeptidyl peptidase-4 inhibitors. Here, we used immunohistochemistry to investigate the pharmacokinetics of alogliptin at the cell and tissue levels in the rat kidney and liver. One hour after alogliptin administration, the most noticeable immunoreactivity in the kidney was a moderate-to-strong staining in proximal tubule S3 segment epithelial cells. On the other hand, immunostaining was found only in the microvilli of S1 and S2 segment cells. Immunoreactivity was also observed in the glomerulus and distal tubules. Positive cells and almost negative cells coexisted in the collecting ducts. Twenty-four hours after administration, moderate immunostaining remained in the S3 segment but staining in other regions had almost disappeared. In the liver 1 hr after administration, hepatocyte staining differed in the hepatic lobule, with zone III being stronger than zone I. Immunostaining had almost disappeared 24 hr after administration. These findings suggest that alogliptin reabsorption at the kidney and uptake at the hepatocyte vary from region to region and that one or more types of transporter are involved in these processes. In addition, long-term alogliptin use may cause the drug to accumulate in S3 segment, leading to adverse events.

Immunohistochemistry for Anti-diabetes Drug, Alogliptin Using a Newly Prepared Monoclonal Antibody: Its Precise Localization in Rat Small Intestine

Knowledge of time sequence of localization of drugs in cells and tissues of animals may help in developing a better understanding of the actual overall pharmacokinetics of the drugs. We produced monoclonal antibody (mAb) against alogliptin (AG), a dipeptidyl peptidase-4 (DPP-4) inhibitor, conjugated to BSA with N-(γ-maleimidobutyryloxy)-succinimide. The mAb was specific for AG and did not cross-react with sitagliptin, vancomycin or amoxicillin. The mAb enabled us to develop an immunohistochemical method for detecting the localization of AG in the rat small intestine. One hour after a single oral administration of AG, immunohistochemistry revealed that the immunoreactivity of AG was observed in almost all of cells and tissues of the duodenum. The microvilli of the absorptive epithelial cells were moderately stained. The staining pattern of AG at jejunum and ilium was almost the same as that of duodenum, but the staining intensity, especially at absorptive epithelial cells and intestinal gland epithelial cells, became stronger towards the distal part of the small intestine. These results suggested that AG may be more actively absorbed from the lower part of the small intestine than in the upper part. It may affect the function of cells with membrane-bound DPP-4 because it was reported that membrane-bound form of DPP-4 exists in the microvilli of the absorptive epithelial cells.

The role of dipeptidylpeptidase-4 inhibitors in management of cardiovascular disease in diabetes; focus on linagliptin

Multiple population based analyses have demonstrated a high incidence of cardiovascular disease (CVD) and cardiovascular (CV) mortality in subjects with T2DM that reduces life expectancy by as much as 15 years. Importantly, the CV system is particularly sensitive to the metabolic and immune derangements present in obese pre-diabetic and diabetic individuals; consequently, CV dysfunction is often the initial CV derangement to occur and promotes the progression to end organ/tissue damage in T2DM. Specifically, diabetic CVD can manifest as microvascular complications, such as nephropathy, retinopathy, and neuropathy, as well as, macrovascular impairments, including ischemic heart disease, peripheral vascular disease, and cerebrovascular disease. Despite some progress in prevention and treatment of CVD, mainly via blood pressure and dyslipidemia control strategies, the impact of metabolic disease on CV outcomes is still a major challenge and persists in proportion to the epidemics of obesity and diabetes. There is abundant pre-clinical and clinical evidence implicating the DPP-4-incretin axis in CVD. In this regard, linagliptin is a unique DPP-4 inhibitor with both CV and renal safety profiles. Moreover, it exerts beneficial CV effects beyond glycemic control and beyond class effects. Linagliptin is protective for both macrovascular and microvascular complications of diabetes in preclinical models, as well as clinical models. Given the role of endothelial-immune cell interactions as one of the key events in the initiation and progression of CVD, linagliptin modulates these cell–cell interactions by affecting two important pathways involving stimulation of NO signaling and potent inhibition of a key immunoregulatory molecule.

The role of renal dipeptidyl peptidase-4 in kidney disease: renal effects of dipeptidyl peptidase-4 inhibitors with a focus on linagliptin

Emerging evidence suggests that dipeptidyl peptidase-4 (DPP-4) inhibitors used to treat type 2 diabetes may have nephroprotective effects beyond the reduced renal risk conferred by glycemic control. DPP-4 is a ubiquitous protein with exopeptidase activity that exists in cell membrane-bound and soluble forms. The kidneys contain the highest levels of DPP-4, which is increased in diabetic nephropathy. DPP-4 inhibitors are a chemically heterogeneous class of drugs with important pharmacological differences. Of the globally marketed DPP-4 inhibitors, linagliptin is of particular interest for diabetic nephropathy as it is the only compound that is not predominantly excreted in the urine. Linagliptin is also the most potent DPP-4 inhibitor, has the highest affinity for this protein, and has the largest volume of distribution; these properties allow linagliptin to penetrate kidney tissue and tightly bind resident DPP-4. In animal models of kidney disease, linagliptin elicited multiple renoprotective effects, including reducing albuminuria, glomerulosclerosis, and tubulointerstitial fibrosis, independent of changes in glucagon-like peptide-1 (GLP-1) and glucose levels. At the molecular level, linagliptin prevented the pro-fibrotic endothelial-to-mesenchymal transition by disrupting the interaction between membrane-bound DPP-4 and integrin β1 that enhances signaling by transforming growth factor-β1 and vascular endothelial growth factor receptor-1. Linagliptin also increased stromal cell derived factor-1 levels, ameliorated endothelial dysfunction, and displayed unique antioxidant effects. Although the nephroprotective effects of linagliptin are yet to be translated to the clinical setting, the ongoing Cardiovascular and Renal Microvascular Outcome Study with Linagliptin in Patients with Type 2 Diabetes Mellitus (CARMELINA®) study will definitively assess the renal effects of this DPP-4 inhibitor. CARMELINA® is the only clinical trial of a DPP-4 inhibitor powered to evaluate kidney outcomes.

Renoprotective effect of DPP-4 inhibitors against free fatty acid-bound albumin-induced renal proximal tubular cell injury

Dipeptidyl peptidase (DPP)-4 inhibitors, a new class of antidiabetic agent, have recently been suggested to exert pleiotropic effects beyond glucose lowering. Renal prognosis in patients with diabetic nephropathy depends on the severity of tubulointerstitial injury induced by massive proteinuria. We thus examined the renoprotective effect of DPP-4 inhibitors on inflammation in cultured mouse proximal tubular cells stimulated with free fatty acid (FFA)-bound albumin. Linagliptin and higher concentrations of sitagliptin, vildagliptin, and alogliptin all inhibited FFA-bound albumin-induced increases in mRNA expression of MCP-1 in cultured mouse proximal tubular cells. Furthermore, linagliptin significantly inhibited tubulointerstitial injury induced by peritoneal injection of FFA-bound albumin, such as inflammation, fibrosis, and apoptosis, in mice without altering systemic characteristics including body weight, fasting blood glucose, and food intake. These results indicate that DPP-4 inhibitors pleiotropically exert a direct renoprotective effect, and may serve as an additional therapeutic strategy to protect proximal tubular cells against proteinuria in patients with diabetic nephropathy.

Linagliptin enhances neural stem cell proliferation after stroke in type 2 diabetic mice

Dipeptidyl peptidase 4 (DPP-4) inhibitors are current drugs for the treatment of type 2 diabetes (T2D) based on their main property to enhance endogenous glucagon-like peptide-1 (GLP-1) levels, thus increasing insulin secretion. However, the mechanism of action of DPP-4 inhibition in extra pancreatic tissues has been poorly investigated and it might occur differently from that induced by GLP-1R agonists. Increased adult neurogenesis by GLP-1R agonists has been suggested to play a role in functional recovery in animal models of brain disorders. We recently showed that the DPP-4 inhibitor linagliptin reduces brain damage after stroke in normal and type 2 diabetic (T2D) mice. The aim of this study was to determine whether linagliptin impacts stroke-induced neurogenesis. T2D was induced by 25 weeks of high-fat diet. Linagliptin treatment was carried out for 7 weeks. Standard diet fed-mice were used as controls. Stroke was induced by middle cerebral artery occlusion 4 weeks into the linagliptin treatment. Neural stem cell (NSC) proliferation/neuroblast formation and striatal neurogenesis/gliogenesis were assessed 3 weeks after stroke. The effect of linagliptin on NSC viability was also determined in vitro. The results show that linagliptin enhances NSC proliferation in T2D mice but not in normal mice. Linagliptin did not increase NSC number in vitro indicating that the effect of linagliptin on NSC proliferation in T2D is indirect. Neurogenesis and gliogenesis were not affected. In conclusion, we found no correlation between acute neuroprotection (occurring in both T2D and normal mice) and increased NSC proliferation (occurring only in T2D mice). However, our results show that linagliptin evokes a differential response on NSC proliferation after stroke in normal and T2D mice suggesting that DPP-4 inhibition effect in the CNS might go beyond the well known increase of GLP-1.

Linagliptin alleviates hepatic steatosis and inflammation in a mouse model of non-alcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH) is a primary cause of cirrhosis and hepatocellular carcinoma. Dipeptidyl peptidase (DPP)-4 inhibitors are established therapies for type 2 diabetes and although DPP-4 inhibitors can reduce hepatic steatosis, their impact on local inflammation and fibrosis in NASH remains unknown. Using two different experimental treatment regimens (4- and 2-week treatments) in streptozotocin-treated neonatal mice on a high-fat diet, we show that the DPP-4 inhibitor linagliptin (10 and 30 mg/kg) significantly attenuated the NAS score from 4.9 ± 0.6 to 3.7 ± 0.4 and 3.6 ± 0.3, respectively, in the 4-week study. In the 2-week study, linagliptin 10 mg/kg significantly reduced NAS score from 4.1 ± 0.4 to 2.4 ± 0.4. Telmisartan was used as a positive control in both studies and lowered NAS score to 1.9 ± 0.7 and 1.4 ± 0.3, respectively. Due to streptozotocin treatment, elevated glucose levels were unchanged by either drug treatment. Further, linagliptin 10 mg/kg significantly reduced mRNA levels of SOCS-3 (from 1.68 ± 0.2 to 0.83 ± 0.08), IFN-γ (from 4.0 ± 0.5 to 2.3 ± 0.3), and TNF-α (from 5.7 ± 0.5 to 2.13 ± 0.3). The latter observation was confirmed by immunohistochemistry of TNF-α in liver specimens. In addition, using microautoradiography, we showed that the distribution of radiolabeled linagliptin was heterogeneous with the highest density associated with interlobular bile ducts and portal tracts (acini). In conclusion, these studies confirm that linagliptin has high exposure in hepatic tissue and has both anti-inflammatory and anti-steatotic activity in NASH.

Linagliptin: A thorough Characterization beyond Its Clinical Efficacy

Linagliptin, one of the five dipeptidyl peptidase-4 inhibitors available, has recently entered the market both in the US and in most European countries for treatment of type 2 diabetes mellitus. It presents a xanthine-based structure, and is characterized by unique pharmacokinetics, with non-linear profile, long terminal half-life allowing prolonged exposure to the drug. It is eliminated predominately through the intestinal tract and only minimally into urine, so that it can be administered, without any dose adjustment, in conditions of renal impairment. Linagliptin is effective in modifying all parameters of hyperglycemia either in monotherapy, or as add-on therapy, together with metformin or a sulfonylurea. It also exhibits a good tolerability profile with few side effects, absence (when used in monotherapy), or low risk (when in combination with a sulfonylurea) of hypoglycemia. More importantly it has a weight neutral effect. A comprehensive report of the literature on linagliptin is provided, paying attention in particular to preclinical studies, interactions with other drugs, safety and tolerability, and results obtained in animal models that highlight properties of linagliptin suggestive of potential additional uses. Particularly promising appear the data demonstrating a positive effect of linagliptin on metabolic dysfunction and renal and/or cardiovascular damage together with more recently reported effects of linagliptin on tissue repair and neuroprotection.

Comparative clinical pharmacokinetics of dipeptidyl peptidase-4 inhibitors

Dipeptidyl peptidase-4 (DPP-4) inhibitors collectively comprise a presently unique form of disease management for persons with type 2 diabetes mellitus. The aim of this review is to compare the clinical pharmacokinetics of available DPP-4 inhibitors (alogliptin, linagliptin, saxagliptin, sitagliptin and vildagliptin) for the purpose of identifying potential selection preferences according to individual patient variables and co-morbidities. DPP-4 inhibitors are readily absorbed orally. Following oral ingestion, absorption occurs mainly in the small intestine, with median times to maximum (peak) plasma concentration ranging from 1 to 3 hours. The fraction of each dose absorbed ranges from approximately 30% with linagliptin to 75-87% for all others. Numerical differences in maximum (peak) plasma drug concentrations and areas under the plasma concentration-time curve among the DPP-4 inhibitors vary by an order of magnitude. However, functional capacity measured in terms of glucose-lowering ability remains comparable among all available DPP-4 inhibitors. Distribution of DPP-4 inhibitors is strongly influenced by both lipophilicity and protein binding. Apparent volumes of distribution (V(d)) for most agents range from 70 to 300 L. Linagliptin exhibits a V(d) of more than 1000 L, indicating widespread distribution into tissues. Binding to target proteins in plasma and peripheral tissues exerts a major influence upon broadening linagliptin distribution. DPP-4 inhibitor metabolism is widely variable, with reported terminal half-lives ranging from approximately 3 to more than 200 hours. Complex relationships between rates of receptor binding and dissociation appear to strongly influence the durations of action of those DPP-4 inhibitors with comparatively shorter half-lives. Durations of activity often are not reflective of clearance and, with the exception of vildagliptin which may be administered either once daily in the evening or twice daily, these medications are effective when used with a once-daily dosing schedule. Saxagliptin and, to a lesser extent, sitagliptin are largely metabolized by hepatic cytochrome P450 (CYP) 3A4 and 3A5 isoforms. With the exception of the primary hydroxylated metabolite of saxagliptin, which is 2-fold less potent than its parent molecule, metabolic products of hepatic biotransformation are minimally active and none appreciably contribute to either the therapeutic or the toxic effects of DPP-4 inhibitors. No DPP-4 inhibitor has been shown to inhibit or to induce hepatic CYP-mediated drug metabolism. Accordingly, the number of clinically significant drug-drug interactions associated with these agents is minimal, with only saxagliptin necessitating dose adjustment if administered concurrently with medications that strongly inhibit CYP3A4. Linagliptin undergoes enterohepatic cycling with a large majority (85%) of the absorbed dose eliminated in faeces via biliary excretion. Other DPP-4 inhibitors predominantly undergo renal excretion, with 60-85% of each dose eliminated as unchanged parent compound in the urine. Systematic reviews of clinical trials suggest that the overall efficacy of DPP-4 inhibitors in patients with type 2 diabetes generally is similar. Apart from these generalizations, pharmacokinetic distinctions that potentially influence product selection are tentative. When considered in total, data reviewed in this report suggest that the best overall balance between potency and the clinical pharmacokinetic characteristics of distribution, metabolism and elimination may be observed with linagliptin followed closely by vildagliptin, saxagliptin, sitagliptin and alogliptin.

Biochemical and histological changes in the small intestine of mice with dextran sulfate sodium colitis

The dextran sulfate sodium (DSS) model of colitis has been commonly utilized in mice to assess novel treatments for ulcerative colitis. Recent studies have indicated that morphological and biochemical changes extend to the small intestine (SI). This study aimed to characterize histological and biochemical changes in the SI during DSS colitis in wild-type (WT) and DPIV knock-out (DPIV(-/-) ) mice treated with saline or the DPIV inhibitors, Ile-Pyrr-(2-CN)*TFA or Ile-Thia. Groups (n = 10) of DPIV(-/-) and WT mice were orally gavaged twice daily with saline, Ile-Pyrr-(2-CN)*TFA or Ile-Thia. Mice consumed 2% DSS in drinking water for 6 days to induce colitis. Small intestinal tissue was assessed for histological changes, sucrase, and DPIV activity and neutrophil infiltration. Jejunal villus length was increased in all groups after 6 days DSS consumption (P < 0.05). Jejunal DPIV activity was significantly lower by 35% in WT mice receiving Ile-Pyrr-(2-CN)*TFA compared to saline controls. Jejunal MPO activity was significantly increased in the WT + saline and DPIV(-/-)  + saline groups following DSS consumption, compared to WT and DPIV(-/-) controls at day 0. Increased sucrase activity was apparent at day 0 in DPIV(-/-) compared to WT mice (P < 0.05). We conclude that DSS-induced damage is not restricted to the colon, but also extends to the small intestine. Furthermore, reduced or absent DPIV activity resulted in functional adaptations to brush border enzyme activity. DPIV inhibitors are now a recognized therapy for type-II diabetes. The work presented here highlights the need to delineate any long-term effects of DPIV inhibitors on SI function, to further validate their safety and tolerability.