Protein kinase C βII in diabetic complications: survey of structural, biological and computational studies

Renoprotective effects of tropisetron through regulation of the TGF-β1, p53 and matrix metalloproteinases in streptozotocin-induced diabetic rats

Renal fibrosis is a major cause of renal failure in diabetic nephropathy. Tropisetron is an antagonist of the 5HT3 receptor that exhibits anti-fibrosis effects. The present research aimed to investigate the protected role of tropisetron against renal fibrosis of diabetic nephropathy and its molecular mechanisms. For this purpose, male Wistar rats were allocated into 5 groups of control, tropisetron, diabetes, tropisetron + diabetes, and glibenclamide + diabetes (n = 7). After induction of type 1 diabetes with a single injection of STZ, tropisetron (3 mg/kg) and glibenclamide (1 mg/kg) were given to the rats daily by intraperitoneal injection for 2 weeks. The obtained data revealed that the treatment of diabetic rats with tropisetron led to a significant decrease in the elevated blood glucose, serum cystatin c, and urinary total protein (UTP) level, indicating the improvement of the impaired kidney function. Moreover, the results of Masson's trichrome staining showed that fibrosis attenuated in the kidney of diabetic rats after tropisetron treatment. RT-PCR and Western blotting revealed that TGF-β1, the apoptotic mediator, and p53 were considerably declined in the kidney of diabetic rats in response to tropisetron treatment. Meanwhile, the expressions of matrix metalloproteinase-9 (MMP-9) and matrix metalloproteinase-2 (MMP-2) were increased. These notable effects were equipotent with glibenclamide, as a standard drug, suggesting that tropisetron can alleviate renal fibrosis in diabetic nephropathy. Our data indicate that tropisetron could improve kidney function and attenuate renal fibrosis through regulation of TGF-β1, p53, and expression of extracellular matrix metalloproteinases.

The C1 domain of Vav3, a novel potential therapeutic target

Vav1/2/3 comprise a protein family with guanyl nucleotide exchange activity for Rho and Rac as well as with motifs conferring adapter activity. Biologically, Vav1 plays a critical role in hematologic cell signaling, whereas Vav2/3 have a wider tissue distribution, but all 3 Vav proteins are implicated in cancer development. A structural feature of Vav1/2/3 is the presence of an atypical C1 domain, which possesses close structural homology to the typical C1 domains of protein kinase C but which fails to bind the second messenger diacylglycerol or the potent analogs, the phorbol esters. Previously, we have shown that five residues in the Vav1 C1 domain are responsible for its lack of phorbol ester binding. Here, we show that the lack of phorbol ester binding of Vav3 has a similar basis. We then explore the consequences of phorbol ester binding to a modified Vav3 in which the C1 domain has been altered to allow phorbol ester binding. We find both disruption of the guanyl nucleotide exchange activity of the modified Vav 3 as well as a shift in localization to the membrane upon phorbol ester treatment. This change in localization is associated with altered interactions with other signaling proteins. The studies provide a first step in assessing the potential for the design of custom C1 domain targeted molecules selective for the atypical C1 domains of Vav family proteins.

Renal damage following Alloxan-induced diabetes is associated with generation of reactive oxygen species, alterations of p53, TGF-β1, and extracellular matrix metalloproteinases in rats

Renal damage is a common problem in diabetes. Alloxan, a potent hyperglycemic and diabetogenic molecule, can induce diabetes through oxidative stress-related mechanisms. Here, we hypothesize that "Alloxan-induced renal damage is associated with alterations of p53, TGF-β1, and extracellular matrix metalloproteinases." To test our hypothesis, we established an animal model (male abino rats) and induced diabetes by intraperitoneal injection of Alloxan monohydrate. Rats with fasting blood glucose level ≥ 200 mg/dL were considered diabetic and were sacrificed after 14, 28, and 42 day intervals. Tissue levels of malondialdehyde and glutathione levels (markers of oxidative stress), and serum MMP-1 were measured. The expression patterns of p53, TGF-β1were evaluated using Western blot and immunohistochemical methods. TIMP-1 expression pattern was determined using RT-PCR and immunohistochemical methods. Alloxan treatment induced histological features of renal damage (inflammation and fibrosis) and was associated with deterioration of the renal functions (elevated blood urea nitrogen and creatinin levels), hyperglycemia, and oxidative stresss (increased malondialdehyde and decreased glutathione levels). There was over-expression of the TGF-β1 protein (profibrogenic protein), p53 (proapoptotic protein), and alterations of extracellular matrix proteins (low level of serum MMP-1 and over-expression of TIMP-1). Alterations of TGF-β, p53, and extracellular matrix metalloproteinases contribute to the pathogenesis of Alloxan-induced renal damage.

Presence and Risk Factors for Glaucoma in Patients with Diabetes

Diabetes mellitus represents a growing international public health issue with a near quadrupling in its worldwide prevalence since 1980. Though it has many known microvascular complications, vision loss from diabetic retinopathy is one of the most devastating for affected individuals. In addition, there is increasing evidence to suggest that diabetic patients have a greater risk for glaucoma as well. Though the pathophysiology of glaucoma is not completely understood, both diabetes and glaucoma appear to share some common risk factors and pathophysiologic similarities with studies also reporting that the presence of diabetes and elevated fasting glucose levels are associated with elevated intraocular pressure-the primary risk factor for glaucomatous optic neuropathy. While no study has completely addressed the possibility of detection bias, most recent epidemiologic evidence suggests that diabetic populations are likely enriched with glaucoma patients. As the association between diabetes and glaucoma becomes better defined, routine evaluation for glaucoma in diabetic patients, particularly in the telemedicine setting, may become a reasonable consideration to reduce the risk of vision loss in these patients.

Multifunctional roles of PKCδ: Opportunities for targeted therapy in human disease

The serine-threonine protein kinase, protein kinase C-δ (PKCδ), is emerging as a bi-functional regulator of cell death and proliferation. Studies in PKCδ-/- mice have confirmed a pro-apoptotic role for this kinase in response to DNA damage and a tumor promoter role in some oncogenic contexts. In non-transformed cells, inhibition of PKCδ suppresses the release of cytochrome c and caspase activation, indicating a function upstream of apoptotic pathways. Data from PKCδ-/- mice demonstrate a role for PKCδ in the execution of DNA damage-induced and physiologic apoptosis. This has led to the important finding that inhibitors of PKCδ can be used therapeutically to reduce irradiation and chemotherapy-induced toxicity. By contrast, PKCδ is a tumor promoter in mouse models of mammary gland and lung cancer, and increased PKCδ expression is a negative prognostic indicator in Her2+ and other subtypes of human breast cancer. Understanding how these distinct functions of PKCδ are regulated is critical for the design of therapeutics to target this pathway. This review will discuss what is currently known about biological roles of PKCδ and prospects for targeting PKCδ in human disease.

Protein kinase C inhibitors: a patent review (2008 - 2009)

INTRODUCTION

The protein kinase C (PKC) is a family of multifunctional isoenzymes involved in apoptosis, migration, adhesion, tumorgenesis, cardiac hypertrophy, angiogenesis, platelet function and inflammation. It also plays a vital role in the regulation of signal transduction, cell proliferation and differentiation through positive and negative regulation of the cell cycle. In this work, we reviewed the existing PKC inhibitors and several patents linked to PKC inhibitors.

AREAS COVERED

Thorough survey on the PKC inhibitors having clinical importance and patents filed for these inhibitors from 2008 - 2009 is reported.

EXPERT OPINION

PKCs are highly potential therapeutic targets for treating diabetic complications, oncological, inflammatory, immunological and dermatological disorders. The clinical trial candidates of PKCs mainly target the catalytic domain, which is highly conserved throughout the PKC family making it difficult to target a particular isoform selectively. Relatively less chemical space and fewer bisubstrate inhibitors targeting both ATP and regulatory domain are explored for PKCs, more research in these areas will be helpful in overcoming existing problems.

Protective effect of short-term genistein supplementation on the early stage in diabetes-induced renal damage

Hyperglycemia-induced oxidative stress has been concerned in the development of diabetic nephropathy (DN), which may cause kidney damage associated with inflammation and fibrosis. This study has been conducted to investigate the role of genistein supplementation in an acute DN state. Mice with FBG levels more than 250 mg/dL after alloxan injection (single i.p., 150 mg/kg) were considered as diabetic. Diabetic mice (DM) were further subdivided according to their FBG levels, medium-high FBG (DMMH < 450 mg/dL) and high FBG (DMH; 450 mg/dL) and were administrated by an AIG-93G diet supplemented with different doses of genistein (0, 0.025 or 0.1%). After 2 weeks' treatment, the levels of kidney malondialdehyde (MDA), blood urea nitrogen (BUN), and plasma creatinine and lipid profiles, as well as oxidative stress and inflammation-related markers, were measured (P < 0.05). Genistein supplementation improved levels of FBG in the DMMH groups, but not in the DMH group, regardless of the treatment dose. Moreover, the supplementation attenuated kidney oxidative stress indicated by MDA, BUN, and plasma creatinine. In addition, genistein treatment decreased inflammatory markers such as nuclear factor kappa B (p65), phosphorylated inhibitory kappa B alpha, C-reactive protein, monocyte chemotactic protein-1, cyclooxygenase-2, and tumor necrosis factor-alpha and improved oxidative stress markers (nuclear-related factor E2, heme oxygenase-1, glutathione peroxidase, and superoxide dismutase isoforms) in treatment groups, regardless of the genistein treatment dose. Furthermore, genistein supplementation inhibited the fibrosis-related markers (protein kinase C, protein kinase C-beta II, and transforming growth factor-beta I) in the DN state. However, 0.1% genistein supplementation in diabetes with high FBG levels selectively showed a preventive effect on kidney damage. These results suggest that genistein might be a good protective substance for DN through regulation of oxidative stress and inflammation. In particular, genistein is more efficient in diabetes patients with medium-high blood glucose levels. Finally, it is required to establish the beneficial dosage of genistein according to blood glucose levels.

Protein kinase C, an elusive therapeutic target?

Protein kinase C (PKC) has been a tantalizing target for drug discovery ever since it was first identified as the receptor for the tumour promoter phorbol ester in 1982. Although initial therapeutic efforts focused on cancer, additional indications--including diabetic complications, heart failure, myocardial infarction, pain and bipolar disorder--were targeted as researchers developed a better understanding of the roles of eight conventional and novel PKC isozymes in health and disease. Unfortunately, both academic and pharmaceutical efforts have yet to result in the approval of a single new drug that specifically targets PKC. Why does PKC remain an elusive drug target? This Review provides a short account of some of the efforts, challenges and opportunities in developing PKC modulators to address unmet clinical needs.