Effects of ethanol on insulin-like growth factor-I system in primary cultured rat hepatocytes: Implications of JNK1/2 and alcoholdehydrogenase

Role of Alcohol Oxidative Metabolism in Its Cardiovascular and Autonomic Effects

Several review articles have been published on the neurobehavioral actions of acetaldehyde and other ethanol metabolites as well as in major alcohol-related disorders such as cancer and liver and lung disease. However, very few reviews dealt with the role of alcohol metabolism in the adverse cardiac and autonomic effects of alcohol and their potential underlying mechanisms, particularly in vulnerable populations. In this chapter, following a brief overview of the dose-related favorable and adverse cardiovascular effects of alcohol, we discuss the role of ethanol metabolism in its adverse effects in the brainstem and heart. Notably, current knowledge dismisses a major role for acetaldehyde in the adverse autonomic and cardiac effects of alcohol because of its low tissue level in vivo. Contrary to these findings in men and male rodents, women and hypertensive individuals are more sensitive to the adverse cardiac effects of similar amounts of alcohol. To understand this discrepancy, we discuss the autonomic and cardiac effects of alcohol and its metabolite acetaldehyde in a model of hypertension, the spontaneously hypertensive rat (SHR) and female rats. We present evidence that enhanced catalase activity, which contributes to cardioprotection in hypertension (compensatory) and in the presence of estrogen (inherent), becomes detrimental due to catalase catalysis of alcohol metabolism to acetaldehyde. Noteworthy, studies in SHRs and in estrogen deprived or replete normotensive rats implicate acetaldehyde in triggering oxidative stress in autonomic nuclei and the heart via (i) the Akt/extracellular signal-regulated kinases (ERK)/nitric oxide synthase (NOS) cascade and (ii) estrogen receptor-alpha (ERα) mediation of the higher catalase activity, which generates higher ethanol-derived acetaldehyde in female heart. The latter is supported by the ability of ERα blockade or catalase inhibition to attenuate alcohol-evoked myocardial oxidative stress and dysfunction. More mechanistic studies are needed to further understand the mechanisms of this public health problem.

Protective effect of short-term treatment with parathyroid hormone 1-34 on oxidative stress is involved in insulin-like growth factor-I and nuclear factor erythroid 2-related factor 2 in rat bone marrow derived mesenchymal stem cells

Bone marrow-derived mesenchymal stem cell (MSC)-mediated regeneration is a promising treatment for degenerative disease and traumatic injuries. MSCs can be isolated from rats using magnetic-activated cell sorting with CD105 antibody. We investigated the relationships between the expression of endogenous insulin-like growth factor-I (IGF-I) and nuclear factor erythroid 2-related factor 2 (Nrf-2) during short-term treatment with parathyroid hormone (PTH) 1-34-induced protective response in MSCs. PTH 1-34 (10(-9)M) decreased reactive oxygen species (ROS) generation but increased cell viability and endogenous IGF-I (p<0.01). Suppression of IGF-I and Nrf-2 using specific small interfering RNA (siRNA) blocked the effects of PTH 1-34. Furthermore, increasing cell viability of PTH against hydrogen peroxide (H2O2) was suppressed by treatment with siRNA to IGF-I and Nr-2 (p<0.05). Exogenous IGF-I (10(-9)M) also increased endogenous IGF-I, cell viability, and Nrf-2 expression. These incremental increases were lessened by Nrf-2 siRNA (p<0.05). Exogenous IGF-I also inhibited the increase of H2O2-induced ROS generation, and the decrease of PTH 1-34-induced ROS generation in the presence of IGF-I and Nrf-2 siRNA. The increase of PTH 1-34-induced Nrf-2 expression was more significant in the nucleus than in the cytosol (p<0.05). PTH 1-34 also inhibited H2O2-induced inducible nitric oxide synthase expression, but increased the expression of heme oxygenase 1/2. The results implicate PTH 1-34, Nrf-2, and IGF-I signaling pathways in the response to oxidative stress. These factors could influence IGF-I regulation of metabolic fate and survival in MSCs.

Role of rostral ventrolateral medullary ERK/JNK/p38 MAPK signaling in the pressor effects of ethanol and its oxidative product acetaldehyde

BACKGROUND

We tested the hypothesis that alterations of the phosphorylation/dephosphorylation profile of mitogen-activated protein kinases (MAPKs) in the rostral ventrolateral medulla (RVLM) underlie the pressor response elicited by ethanol (EtOH) microinjection into the RVLM of spontaneously hypertensive rats (SHRs). The studies were extended to determine whether acetaldehyde (ACA), the primary oxidative product of EtOH, replicates the molecular effects of EtOH within the RVLM and the consequent pressor response.

METHODS

Effects of EtOH or ACA on blood pressure (BP) were evaluated in the absence or presence of selective JNK (SP600125), ERK (PD98059), p38 (SB203580), or ser/thr phosphatases (okadaic acid [OKA]) inhibitor.

RESULTS

Intra-RVLM EtOH (10 μg/rat) or ACA (2 μg/rat) caused a similar ERK2-dependent pressor response because EtOH or ACA-evoked increases in BP and in RVLM p-ERK2 level were abolished after pharmacologic inhibition of ERK phosphorylation. SP600125 abrogated the pressor action of EtOH, but not ACA, thus implicating JNK in EtOH action on BP. Despite EtOH enhancement of p38 phosphorylation, pharmacological studies argued against a causal role for this kinase in EtOH-evoked pressor response. RVLM phosphatase catalytic activity was not influenced by EtOH or ACA. Interestingly, pharmacologic phosphatase inhibition (OKA), which increased RVLM p-ERK2 and BP, abrogated the pressor effect of subsequently administered EtOH or ACA.

CONCLUSIONS

Enhancement of RVLM ERK2 phosphorylation constitutes a major molecular mechanism for the pressor response elicited by intra-RVLM EtOH or its metabolite, ACA, in conscious SHRs. Further, RVLM kinases dephosphorylation does not contribute to intra-RVLM EtOH- or ACA-evoked pressor response.

Protective effect of polysaccharide from Hizikia fusiformis against ethanol-induced toxicity

Polysaccharide extracted from Hizikia fusiformis (Hf-PS-1) exhibited protective effects against ethanol-induced peptic injury. In in vivo assay, the ethanol group exhibited decrease of total glutathione (GSH) and increase of jun N-terminal kinase (JNK) phosphorylation relative to the control group, whereas levels were significantly increased and decreased, respectively, in the Hf-PS-1 group. Hf-PS-1 reduced ethanol-induced gastric injury. In in vitro assay, ethanol induced IEC-6 cells' death in a dose-dependent manner. Ethanol decreased the phosphorylation of Shc and the binding of Grb2 to Shc, and Hf-PS-1 pretreatment increased them. Ethanol also induced the phosphorylation of JNK and extracellular signal-regulated kinase (ERK), whereas Hf-PS-1 pretreatment decreased JNK activation but not ERK. Co-treatment with JNK inhibitor and ethanol decreased GSH levels, indicating that JNK phosphorylation is a critical factor during ethanol-induced injury. Therefore, Hf-PS-1 may be useful to protect against ethanol-induced gastrointestinal injury.

Protective effect of a polysaccharide from Hizikia fusiformis against ethanol-induced cytotoxicity in IEC-6 cells

In the present study, we examined the signaling pathways related to the ethanol-protective effect of Hf-PS-1 in IEC-6 cells. Ethanol induced the death of IEC-6 cells in a dose-dependent manner, and pretreatment with Hf-PS-1 abrogated the ethanol toxicity. When we examined whether the effect of Hf-PS-1 on ethanol cytotoxicity was associated with insulin growth factor-I receptor signaling pathways, involving mitogen-activated protein kinase (MAPK), we found that ethanol treatment decreased the phosphorylation of Shc and the binding of Grb2 to Shc, and Hf-PS-1 pretreatment increased them. Ethanol treatment also induced the phosphorylation of JNK and ERK, whereas Hf-PS-1 pretreatment decreased JNK activation but not ERK activation. Using a JNK inhibitor (SP600125), we examined GSH levels to determine whether Hf-PS-1 pretreatment mi20 ght protect against ethanol-induced gastric intestinal damage by down-regulating JNK. Co-treatment with SP600125 and ethanol decreased GSH levels, indicating that JNK phosphorylation is a critical factor during ethanol-induced injury and that the effect of Hf-PS-1 occurs via JNK down-regulation. We have thus demonstrated the protective effect of Hf-PS-1 against ethanol-induced cellular damage. Therefore, Hf-PS-1 may be useful as a bio-functional food source to protect against ethanol-induced gastrointestinal injury.

Alcohol consumption impairs hepatic protein trafficking: mechanisms and consequences

Alcoholic liver disease is a major biomedical health concern in the United States. Despite considerable research efforts aimed at understanding the progression of the disease, the specific mechanisms leading to alcohol-induced damage remain elusive. Numerous proteins are known to have alcohol-induced alterations in their dynamics. Defining these defects in protein trafficking is an active area of research. In general, two trafficking pathways are affected: transport of newly synthesized secretory or membrane glycoproteins from the Golgi to the basolateral membrane and clathrin-mediated endocytosis from the sinusoidal surface. Both impaired secretion and internalization require ethanol metabolism and are likely mediated by acetaldehyde. Although the mechanisms by which ethanol exposure impairs protein trafficking are not fully understood, recent work implicates alcohol-induced modifications on tubulin or components of the clathrin machinery as potential mediators. Furthermore, the physiological ramifications of impaired protein trafficking are not fully understood. In this review, we will list and discuss the proteins whose trafficking patterns are known to be impaired by ethanol exposure. We will then describe what is known about the possible mechanisms leading to impaired protein trafficking and how disrupted protein trafficking alters liver function and may explain clinical features of the alcoholic patient.

Direct actions of cortisol, thyroxine and growth hormone on IGF-I mRNA expression in sea bream hepatocytes

The present study aims to investigate potential regulatory effect of different growth-related hormones including growth hormone (GH), human insulin-like growth factor-I (hIGF-I), thyroxine (T(4)), triiodothyronine (T(3)) and cortisol, on insulin-like growth factor-I (IGF-I) mRNA expression of hepatocytes isolated from silver sea bream. By using real-time PCR, IGF-I mRNA expression profiles of hepatocytes in response to individual hormones were determined in vitro. Hepatocytes incubated with GH at concentrations of 10-1000 ng/mL showed significantly higher IGF-I expression, but the elevation was attenuated at high concentration of GH (1000 ng/mL). IGF-I expression remained unchanged in hepatocytes after incubation with hIGF-I. Hepatocytes incubated with T(4) at concentration of 1000 ng/mL exhibited a significant elevation in IGF-I expression, whereas no difference in IGF-I expression was demonstrated in hepatocytes after incubation with T(3). Upon incubation with cortisol (1-1000 ng/mL), IGF-I expression was significantly decreased in hepatocytes in a dose-dependent manner. Our study demonstrated that GH, T(4), and cortisol had direct modulatory effects on IGF-I expression in fish hepatocytes in vitro.