Age-related changes in serum levels of insulin-like growth factor-II and its binding proteins correlate with calcaneal bone mineral density among post-menopausal South-Indian women.

BACKGROUND: Insulin-like growth factor (IGF) system components are important regulators of bone metabolism, which have a predominant role in determining bone mineral density (BMD). While the serum levels of IGF-I are regulated by various systemic hormones and growth factors, IGF-II levels reflect the skeletal production relative to physical activity, mechanical loading, aging, race etc. Though various studies have been carried out among women of different ethnic groups to understand the relationship between serum levels of IGF-II and BMD, the results seem to be quite inconclusive. METHODS: We evaluated the same, recruiting South-Indian women who engage themselves in a wide variety of physical activities pertaining to their profession and life style. RESULTS: Serum levels of IGF-II and IGF binding protein (IGFBP)-3 showed positive correlation with calcaneal BMD, whereas IGFBP-4 showed negative correlation. These IGF system components exhibited similar correlations with serum bone formation markers and opposite trend with bone resorption marker. While both IGF-II and IGFBP-3 levels were observed to be decreased with aging and menopause, IGFBP-4 levels increased. CONCLUSIONS: The alterations in serum levels of IGF-II and its binding proteins due to aging and menopause could be some of the major contributors of decreased calcaneal BMD observed among elderly women.

Exploiting tyrosinase expression and activity in melanocytic tumors: quercetin and the central role of p53.

Melanoma is an aggressive tumor that expresses the pigmentation enzyme tyrosinase. Tyrosinase expression increases during tumorigenesis, which could allow for selective treatment of this tumor type by strategies that use tyrosinase activity. Approaches targeting tyrosinase would involve gene transcription or signal transduction pathways mediated by p53 in a direct or indirect manner. Two pathways are proposed for exploiting tyrosinase expression: (a) a p53-dependent pathway leading to apoptosis or arrest and (b) a reactive oxygen species-mediated induction of endoplasmic reticulum stress in p53 mutant tumors. Both strategies could use tyrosinase-mediated activation of quercetin, a dietary polyphenol that induces the expression of p53 and modulates reactive oxygen species. In addition to antitumor signaling properties, activation of quercetin could complement conventional cancer therapy by the induction of phase II detoxification enzymes resulting in p53 stabilization and transduction of its downstream targets. In conclusion, recent advances in tyrosinase enzymology, prodrug chemistry, and modern chemotherapeutics present an intriguing and selective multitherapy targeting system where dietary bioflavonoids could be used to complement conventional cancer treatments.

Quercetin abrogates chemoresistance in melanoma cells by modulating deltaNp73.

BACKGROUND: The alkylating agent dacarbazine (DTIC) has been used in the treatment of melanoma for decades, but when used as a monotherapy for cancer only moderate response rates are achieved. Recently, the clinical use of temozolomide (TMZ) has become the more commonly used analog of DTIC-related oral agents because of its greater bioavailability and ability to cross the blood brain barrier. The response rates achieved by TMZ are also unsatisfactory, so there is great interest in identifying compounds that could be used in combination therapy. We have previously demonstrated that the bioflavonoid quercetin (Qct) promoted a p53-mediated response and sensitized melanoma to DTIC. Here we demonstrate that Qct also sensitizes cells to TMZ and propose a mechanism that involves the modulation of a truncated p53 family member, deltaNp73. METHODS: DB-1 melanoma (p53 wildtype), and SK Mel 28 (p53 mutant) cell lines were treated with TMZ (400 microM) for 48 hrs followed by Qct (75 microM) for 24 hrs. Cell death was determined by Annexin V-FITC staining and immunocytochemical analysis was carried out to determine protein translocation. RESULTS: After treatment with TMZ, DB-1 cells demonstrated increased phosphorylation of ataxia telangiectasia mutated (ATM) and p53. However, the cells were resistant to TMZ-induced apoptosis and the resistance was associated with an increase in nuclear localization of deltaNp73. Qct treatment in combination with TMZ abolished drug insensitivity and caused a more than additive induction of apoptosis compared to either treatment alone. Treatment with Qct, caused redistribution of deltaNp73 into the cytoplasm and nucleus, which has been associated with increased p53 transcriptional activity. Knockdown of deltaNp73 restored PARP cleavage in the TMZ treated cells, confirming its anti-apoptotic role. The response to treatment was predominantly p53 mediated as the p53 mutant SK Mel 28 cells showed no significant enhancement of apoptosis. CONCLUSION: This study demonstrates that Qct can sensitize cells to TMZ and that the mechanisms of sensitization involve modulation of p53 family members.

L-carnitine mediates protection against DNA damage in lymphocytes of aged rats.

It has been proposed that age-associated disorders are related to a time-dependent shift in the antioxidant/prooxidant balance towards oxidative damage. Increased production of oxidants in vivo can cause damage to intracellular macromolecules such as DNA, proteins and lipids, which can in turn lead to oxidative injury. Carnitine is a vitamin-like compound that serves as a carrier to transport long-chain fatty acids into the mitochondria for beta-oxidation. In the present study, the effect of L-carnitine, a widely recognized essential nutrient, was evaluated on the status of lipid peroxidation and certain antioxidant enzymes and DNA damage in lymphocytes with relation to age in male wistar rats. The levels of lipid peroxides were remarkably increased whereas, the activities of antioxidant enzymes were significantly decreased in aged control animals when compared to younger controls. In aged animals, administration of L-carnitine for 21 days significantly decreased the levels of lipid peroxides and improved the activities of antioxidant enzymes like superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase. L-Carnitine enhanced T-cell proliferative responses as evaluated by T-cell proliferation assay using [3H] thymidine incorporation and also significantly reduced DNA damage, apoptosis and TNF-alpha level in lymphocytes of aged animals. Our results suggest that L -carnitine may have a vital role in improving functions in the cells of the immune system particularly the lymphocytes possibly through its antioxidant action.

Tyrosinase overexpression promotes ATM-dependent p53 phosphorylation by quercetin and sensitizes melanoma cells to dacarbazine.

Dacarbazine (DTIC) has been used for the treatment of melanoma for decades. However, monotherapy with this chemotherapeutic agent results only in moderate response rates. To improve tumor response to DTIC current clinical trials in melanoma focus on combining a novel targeted agent with chemotherapy. Here, we demonstrate that tyrosinase which is commonly overexpressed in melanoma activates the bioflavonoid quercetin (Qct) and promotes an ataxia telangiectasia mutated (ATM)-dependent DNA damage response. This response sensitizes melanoma cells that overexpress tyrosinase to DTIC. In DB-1 melanoma cells that overexpress tyrosinase (Tyr(+) cells), the threshold for phosphorylation of ATM and p53 at serine 15 was observed at a low dose of Qct (25 microM) when compared to the mock transfected pcDNA3 cells, which required a higher dose (75 microM). Both pcDNA3 and Tyr(+) DB-1 cells demonstrated similar increases in phosphorylation of p53 at other serine sites, but in the Tyr(+) cells, DNApk expression was found to be reduced compared to control cells, indicating a shift towards an ATM-mediated response. The DB-1 control cells were resistant to DTIC, but were sensitized to apoptosis with high dose Qct, while Tyr(+) cells were sensitized to DTIC with low or high dose Qct. Qct also sensitized SK Mel 5 (p53 wildtype) and 28 (p53 mutant) cells to DTIC. However, when SK Mel 5 cells were transiently transfected with tyrosinase and treated with Qct plus DTIC, SK Mel 5 cells demonstrated a more than additive induction of apoptosis. Therefore, this study demonstrates that tyrosinase overexpression promotes an ATM-dependent p53 phosphorylation by Qct treatment and sensitizes melanoma cells to dacarbazine. In conclusion, these results suggest that Qct or Qct analogues may significantly improve DTIC response rates in tumors that express tyrosinase.

Role of L-carnitine in the modulation of immune response in aged rats.

BACKGROUND: The immune system undergoes alterations in functions with aging which results in progressive deterioration in the ability to respond to infection. The importance of nutrients in regulating immune responses has widened attempts on interventions that improve immune functions with aging. L-carnitine serves as a vital factor in the mitochondrial transport of fatty acids, a process essential for fatty acid oxidation and energy release. L-carnitine is categorized as a conditionally essential nutrient factor and its concentrations are reported to be decreased with aging. METHODS: The immunomodulatory role of L-carnitine was assessed in aged rats after administration of L-carnitine (300 mg/kg body weight/day) for 7, 14 and 21 days by evaluating neutrophil functions, delayed-type hypersensitivity (DTH) responses and immunoglobulin concentrations. RESULTS: Aged animals exhibited decreased non-specific immune functions, delayed-type hypersensitivity responses and immunoglobulin concentrations compared to younger controls. Treatment with L-carnitine improved neutrophil functions, delayed-type hypersensitivity responses and the concentrations of immunoglobulins A and G in aged animals in a significant manner. However L-carnitine treatment did not have any impact on IgM concentration and type responses. CONCLUSIONS: This study demonstrated that aging is associated with a decline in immune functions and supplementing L-carnitine had a positive effect in improving immune responses in aged animals.

Quercetin selectively inhibits bioreduction and enhances apoptosis in melanoma cells that overexpress tyrosinase.

Tyrosinase is expressed in melanoma cells and catalyzes the formation of 3,3',4',5,7-pentahydroxyflavone (quercetin) into reactive quinone species and subsequent glutathionyl adducts. Therefore, we examined the effect of quercetin metabolism on the glutathione (GSH) bioreduction pathway and cell viability in DB-1 melanoma cells that express varying levels of tyrosinase (Tyr+). In a cell-free system, GSH was significantly decreased by quercetin, which coincided with the formation of glutathionyl adducts. In Tyr+ clones, quercetin decreased bioreduction capacity and increased reactive oxygen species (ROS) to a greater degree compared to control cells. The antioxidant/electrophile response element-induced enzymes, glutathione-S-transferase (GST), and nicotinamide adenine dinucleotide phosphate:quinone oxidoreductase 1 were expressed at high levels in Tyr+ cells and contributed to pro-oxidant quercetin metabolism. The basal level of ROS and apoptosis was higher in Tyr+ cells and were selectively increased after exposure to quercetin. The increase in apoptosis following quercetin exposure was p53/Bax mediated and correlated with a decrease in GST-driven bioreduction capacity and an increase in ROS. In conclusion, quercetin can selectively sensitize Tyr+ expressing melanoma cells to apoptosis and may serve as an adjuvant to chemotherapy by enhancing cell death and interfering with GST-mediated drug resistance.

Transforming growth factor -beta receptor signaling in cancer.

Transforming growth factor-beta (TGF-beta) is an ubiquitous cytokine that affects various biological processes, such as regulation of cell proliferation, immune responses, growth, differentiation, angiogenesis, and apoptosis of various cell types. The TGF-beta ligand initiates signaling by binding to and joining type I and II receptors of serine/threonine kinases. This review discusses the TGF-beta ligands and receptors, its positive and negative regulators in signaling, as well as its important roles with respect to tumor suppression and progression.