Haseeb Ahsan

Role of Bcl-2 family proteins and caspases in the regulation of apoptosis

Apoptosis, or programmed cell death, plays a pivotal role in the elimination of unwanted, damaged, or infected cells in multicellular organisms and also in diverse biological processes, including development, cell differentiation, and proliferation. Apoptosis is a highly regulated form of cell death, and dysregulation of apoptosis results in pathological conditions including cancer, autoimmune and neurodegenerative diseases. The Bcl-2 family proteins are key regulators of apoptosis, which include both anti- and pro-apoptotic proteins, and a slight change in the dynamic balance of these proteins may result either in inhibition or promotion of cell death. Execution of apoptosis by various stimuli is initiated by activating either intrinsic or extrinsic pathways which lead to a series of downstream cascade of events, releasing of various apoptotic mediators from mitochondria and activation of caspases, important for the cell fate. In view of recent research advances about underlying mechanism of apoptosis, this review highlights the basics concept of apoptosis and its regulation by Bcl-2 family of protein. Furthermore, this review discusses the interplay of various apoptotic mediators and caspases to decide the fate of the cell. We expect that this review will add to the pool of basic information necessary to understand the mechanism of apoptosis which may implicate in designing better strategy to develop biomedical therapy to control apoptosis.

Alpha‐2‐macroglobulin: A physiological guardian

Alpha macroglobulins are large glycoproteins which are present in the body fluids of both invertebrates and vertebrates. Alpha‐2‐macroglobulin (α2M), a key member of alpha macroglobulin superfamily, is a high‐molecular weight homotetrameric glycoprotein. α2M has many diversified and complex functions, but it is primarily known by its ability to inhibit a broad spectrum of proteases without the direct blockage of the protease active site. α2M is also known to be involved in the regulation, transport, and a host of other functions. For example, apart from inhibiting proteinases, it regulates binding of transferrin to its surface receptor, binds defensin and myelin basic protein, etc., binds several important cytokines, including basic fibroblast growth factor (bFGF), platelet‐derived growth factor (PDGF), nerve growth factor (NGF), interleukin‐1β (IL‐1β), and interleukin‐6 (IL‐6), and modify their biological activity. α2M also binds a number of hormones and regulates their activity. α2M is said to protect the body against various infections, and hence, can be used as a biomarker for the diagnosis and prognosis of a number of diseases. However, this multipurpose antiproteinse is not “fail safe” and could be damaged by reactive species generated endogenously or exogenously, leading to various pathophysiological conditions. J. Cell. Physiol. 228: 1665–1675, 2013.

Pharmacological potential of tocotrienols: a review

Tocotrienols, members of the vitamin E family, are natural compounds found in a number of vegetable oils, wheat germ, barley, and certain types of nuts and grains. Like tocopherols, tocotrienols are also of four types viz. alpha, beta, gamma and delta. Unlike tocopherols, tocotrienols are unsaturated and possess an isoprenoid side chain. Tocopherols are lipophilic in nature and are found in association with lipoproteins, fat deposits and cellular membranes and protect the polyunsaturated fatty acids from peroxidation reactions. The unsaturated chain of tocotrienol allows an efficient penetration into tissues that have saturated fatty layers such as the brain and liver. Recent mechanistic studies indicate that other forms of vitamin E, such as γ-tocopherol, δ-tocopherol, and γ-tocotrienol, have unique antioxidant and anti-inflammatory properties that are superior to those of α-tocopherol against chronic diseases. These forms scavenge reactive nitrogen species, inhibit cyclooxygenase- and 5-lipoxygenase-catalyzed eicosanoids and suppress proinflammatory signalling, such as NF-κB and STAT. The animal and human studies show tocotrienols may be useful against inflammation-associated diseases. Many of the functions of tocotrienols are related to its antioxidant properties and its varied effects are due to it behaving as a signalling molecule. Tocotrienols exhibit biological activities that are also exhibited by tocopherols, such as neuroprotective, anti-cancer, anti-inflammatory and cholesterol lowering properties. Hence, effort has been made to compile the different functions and properties of tocotrienols in experimental model systems and humans. This article constitutes an in-depth review of the pharmacology, metabolism, toxicology and biosafety aspects of tocotrienols. Tocotrienols are detectable at appreciable levels in the plasma after supplementations. However, there is inadequate data on the plasma concentrations of tocotrienols that are sufficient to demonstrate significant physiological effect and biodistribution studies show their accumulation in vital organs of the body. Considering the wide range of benefits that tocotrienols possesses against some common human ailments and having a promising potential, the experimental analysis accounts for about a small fraction of all vitamin E research. The current state of knowledge deserves further investigation into this lesser known form of vitamin E.

3-Nitrotyrosine: A biomarker of nitrogen free radical species modified proteins in systemic autoimmunogenic conditions

The free radical-mediated damage to proteins results in the modification of amino acid residues, cross-linking of side chains and fragmentation. l-Tyrosine and protein bound tyrosine are prone to attack by various mediators and reactive nitrogen intermediates to form 3-nitrotyrosine (3-NT). Activated macrophages produce superoxide (O2(·-)) and NO, which are converted to peroxynitrite ONO2(-). 3-NT formation is also catalyzed by a class of peroxidases utilizing nitrite and hydrogen peroxide as substrates. Evidence supports the formation of 3-NT in vivo in diverse pathologic conditions and 3-NT is thought to be a relatively specific marker of oxidative damage mediated by peroxynitrite. Free/protein-bound tyrosines are attacked by various RNS, including peroxynitrite, to form free/protein-bound 3-NT, which may provide insight into the etiopathogenesis of autoimmune conditions. The formation of nitrotyrosine represents a specific peroxynitrite-mediated protein modification; thus, detection of nitrotyrosine in proteins is considered as a biomarker for endogenous peroxynitrite activity. The peroxynitrite-driven oxidation and nitration of biomolecules may lead to autoimmune diseases such as systemic lupus. The subsequent release of altered proteins may enable them to act as antigen-inducing antibodies against self-proteins. Hence, tyrosine nitrated proteins can act as neoantigens and lead to the generation of autoantibodies against self proteins in various autoimmune disorders.

Diabetic retinopathy--biomolecules and multiple pathophysiology.

One of the major complications in patients with diabetes is diabetic retinopathy (DR), a leading cause of blindness worldwide. It causes visual impairment and finally blindness, a result of long-term accumulated damage to the small blood vessels in the retina. It takes several years before any clinical symptoms of retinopathy appear in diabetic patients. Consequently, glycemic control, blood pressure and lipid-lowering therapy have all shown benefits in reducing the incidence and progression of DR. A number of hyperglycemia-induced metabolic stresses have been implicated in the pathophysiology of DR. The microvasculature of the retina responds to hyperglycemia through a number of biochemical changes, including the activation of protein kinase C (PKC), increased advanced glycation end-products (AGEs) formation, polyol pathway and oxidative stress. There is an accumulating body of evidence indicating that inflammation and neurodegeneration play an important role in the pathogenesis of DR.

Protective effects of tocotrienols against lipid-induced nephropathy in experimental type-2 diabetic rats by modulation in TGF-β expression

Dyslipidemia is common in patients with diabetes mellitus (DM) and is considered a risk factor for the progression of diabetic nephropathy (DN). Hyperlipidemia and hyperglycemia act synergistically to induce renal injury. The present study was designed to investigate the protective effects of tocotrienols as tocotrienol-rich fraction (TRF) extracted from palm (PO) and rice bran oils (RBO) against lipid induced nephropathy in type-2 diabetic rats and its probable molecular mechanism. Male Wistar rats (175-200 g) were divided into four groups. The first group served as diabetic control, while the second and third groups received PO-TRF and RBO-TRF, respectively by gavage over a period of sixteen weeks post-induction of diabetes. The fourth group comprised of age-matched rats that served as normal control. The effects of TRF on serum lipid profile, oxidative stress markers, expression of TGF-β, fibronectin and collagen type IV were analyzed in the kidney of diabetic rats. Treatment with PO-TRF and RBO-TRF significantly improved glycemic status, serum lipid profile and renal function in type-2 diabetic rats. In addition, TRF supplementation down-regulated the expression of TGF-β, fibronectin and collagen type IV in the kidney of diabetic rats. Transforming growth factor-β (TGF-β) plays a critical role in progression of DN, but its modulation by tocotrienols in DN remains unexplored. TRF ameliorated lipid induced nephropathy in type-2 diabetes by its hypoglycemic, hypolipidemic and antioxidant activities as well as by modulation of TGF-β to prevent increased expression of collagen type IV and fibrinogen. We finally propose a mechanism for the expression of molecular markers that are significant in the events leading to diabetic nephropathy and its modulation by tocotrienols/TRF.

A review of characterization of tocotrienols from plant oils and foods

Tocotrienols, members of the vitamin E family, are natural compounds found in a number of vegetable oils, wheat germ, barley and certain types of nuts and grains. Vegetable oils provide the best sources of these vitamin E forms, particularly palm oil and rice bran oil contain higher amounts of tocotrienols. Other sources of tocotrienols include grape fruit seed oil, oats, hazelnuts, maize, olive oil, buckthorn berry, rye, flax seed oil, poppy seed oil and sunflower oil. Tocotrienols are of four types, viz. alpha (α), beta (β), gamma (γ) and delta (δ). Unlike tocopherols, tocotrienols are unsaturated and possess an isoprenoid side chain. A number of researchers have developed methods for the extraction, analysis, identification and quantification of different types of vitamin E compounds. This article constitutes an in-depth review of the chemistry and extraction of the unsaturated vitamin E derivatives, tocotrienols, from various sources using different methods. This review article lists the different techniques that are used in the characterization and purification of tocotrienols such as soxhlet and solid–liquid extractions, saponification method, chromatography (thin layer, column chromatography, gas chromatography, supercritical fluid, high performance), capillary electrochromatography and mass spectrometry. Some of the methods described were able to identify one form or type while others could analyse all the analogues of tocotrienol molecules. Hence, this article will be helpful in understanding the various methods used in the characterization of this lesser known vitamin E variant.

Role of peroxynitrite-modified biomolecules in the etiopathogenesis of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic inflammatory autoimmune disease characterized by autoantibodies directed against various biomolecules. The initial immunogens that drive the development of SLE are unknown, but characteristics of the immune response in SLE suggest that it is an antigen-driven response, and a chromatin antigen could be one of the immunogens for the production of antinuclear antibodies (ANA) in SLE. Other factors implicated in the pathogenesis of SLE include nitrogen-free radicals such as nitric oxide and peroxynitrite. The free radical-mediated damage to proteins results in the modification of amino acid residues, cross-linking of side chains and fragmentation. The tyrosine residues in proteins are susceptible to attack by various reactive nitrogen intermediates, including peroxynitrite to form 3-nitrotyrosine (3-NT). The presence of nitrated proteins in vivo indicates that peptides derived from the proteolytic degradation of modified proteins could serve as neoantigens. Histones are highly conserved proteins that are rich in basic amino acids lysine and arginine. Autoantibodies against histones and anti-DNA antibodies are present in SLE. The anti-DNA autoantibodies coexist with anti-histone autoantibodies and may react with chromatin-associated histones and histone complexes. Elevated levels of reactive nitrogen species (RNS) in SLE patients suggest a possible role in the pathogenesis of the disease. The alteration of proteins resulting from photomodification or peroxynitrite could lead to the development of antibodies. Therefore, the modified proteins or photoadducts could have important implications in autoimmunity, and understanding the pathophysiology of peroxynitrite-modified biomolecules could lead to a better understanding of autoimmune phenomenon in SLE.

Prophylactic effect of baicalein against renal dysfunction in type 2 diabetic rats

Despite a tremendous advancement in the management of diabetes mellitus, diabetic nephropathy (DN) is still a significant problem for many patients with diabetes, because of the inefficacy and associated side effects of pharmacological drugs. There is a demand for new therapeutic drugs which on one hand efficiently prevent the development of DN by targeting several metabolic and inflammatory pathways, and on the other hand, are side-effect free. In recent years, many researchers have suggested that inflammation plays an important role in the development of DN, hence, NF-κB has received much attention. We investigated the nephroptotective effects of baicalein (BAC), a flavonoid, in high fat diet/streptozotocin induced type 2 diabetic Wistar rats. BAC (10 mg/kg bw/day and 20 mg/kg bw/day) treatment was given to the diabetic rats by oral gavage for 16 weeks post induction of diabetes. The effect of BAC was compared to a commercial antidiabetic drug rosiglitazone (RZ, 3 mg/kg bw/day). BAC and RZ treatment significantly lowered food intake, body weight and levels of fasting blood glucose, HbA1c and homeostasis model assessment index (HOMA-IR) in diabetic rats. Both, BAC and RZ restored normal renal function and mitigated renal oxidative stress. BAC and RZ also suppressed the activation of NF-κB, decreased expression of iNOS and TGF-β1, and ameliorated the structural changes in renal tissues. Moreover, BAC also normalized the levels of serum pro-inflammatory cytokines and liver function enzymes. However, rosiglitazone treatment produced liver toxicity as was evident from increased serum levels of liver function enzymes; ALP, SGOT and SGPT. Taken together, BAC treatment preserved renal function by anti-hyperglycemic, antioxidant and anti-inflammatory effects. Moreover, BAC was found to be more effective as compared to RZ, suggesting the efficacy of BAC in the treatment of DN.

Reactive oxygen species and anti-proteinases

Abstract Reactive oxygen species (ROS) cause damage to macromolecules such as proteins, lipids and DNA and alters their structure and function. When generated outside the cell, ROS can induce damage to anti-proteinases. Anti-proteinases are proteins that are involved in the control and regulation of proteolytic enzymes. The damage caused to anti-proteinase barrier disturbs the proteinase-anti-proteinases balance and uncontrolled proteolysis at the site of injury promotes tissue damage. Studies have shown that ROS damages anti-proteinase shield of the body by inactivating key members such as alpha-2-macroglobulin, alpha-1-antitrypsin. Hypochlorous acid inactivates α-1-antitrypsin by oxidizing a critical reactive methionine residue. Superoxide and hypochlorous acid are physiological inactivators of alpha-2-macroglobulin. The damage to anti-proteinase barrier induced by ROS is a hallmark of diseases such as atherosclerosis, emphysema and rheumatoid arthritis. Thus, understanding the behaviour of ROS-induced damage to anti-proteinases may helps us in development of strategies that could control these inflammatory reactions and diseases.