Ethanol inhibits some of the early effects of epidermal growth factor in vivo

Fetal alcohol syndrome and developing craniofacial and dental structures--a review

OBJECTIVES

Fetal alcohol syndrome (FAS) is a collection of signs and symptoms seen in children exposed to alcohol in the prenatal period. It is characterized mainly by a distinct pattern of craniofacial malformations, physical and mental retardation. However, with the increased incidence of FAS, there is a great variation in the clinical features of FAS.

DESIGN

Narrative review.

RESULTS

This review describes data from clinical and experimental studies, and in vitro models. Experimental studies have shown that alcohol has a direct toxic effect on the ectodermal and mesodermal cells of the developing embryo, particularly in the cells destined to give rise to dentofacial structures (i.e. cranial neural crest cells). Other effects, such as, abnormal pattern of cranial and mandibular growth and altered odontogenesis are described in detail. The exact mechanism by which alcohol induces its teratogenic effects remains still unknown. The possible mechanisms are outlined here, with an emphasis on the developing face and tooth. Possible future research directions and treatment strategies are also discussed.

CONCLUSION

Early identification of children affected by prenatal alcohol exposure leads to interventions, services, and improved outcomes. FAS can be prevented with the elimination of alcohol consumption during pregnancy. We need to provide education, target high-risk groups, and make this issue a high priority in terms of public health.

Decreased binding and autophosphorylation of the epidermal growth factor receptor in ethanol-fed rats

We have shown previously that binding and processing of epidermal growth factor are impaired in livers of ethanol-fed rats. In the current study, we examined these ethanol-induced alterations in greater detail by studying both high and low affinity epidermal growth factor binding as well as the ability of added ligand to stimulate receptor autophosphorylation. We also measured the binding of anti-receptor antibody to intact and permeabilized cells in order to determine more accurately the levels of receptor protein. Hepatocytes were isolated from ethanol-fed and pair-fed control rats. Ligand binding, antibody binding, and ligand-induced receptor autrophosphorylation were measured in the respective cell populations. In ethanol-fed animals, binding to both high and low affinity states of the hepatic epidermal growth factor receptor was decreased by 40-50% (P < 0.01). This ethanol-induced decrease in ligand binding was accompanied by a reduced ability of epidermal growth factor to stimulate receptor autophosphorylation (32% decrease, P < 0.01). In contrast, binding of anti-receptor antibody was not altered in ethanol-fed animals. In conclusion, chronic ethanol feeding decreased epidermal growth factor binding with a concomitant decrease in the ability of the receptor tyrosine kinase to phosphorylate tyrosine residues. These changes were not accompanied by an actual decrease in receptor protein content. These findings could be relevant to modified responses to this growth factor in the livers of chronic ethanol-fed animals.

Recent Advances in Pharmacological Research on Alcohol

Alcohol dependence is a major public health problem. Studies have shown that a person dependent on alcohol often coabuses other substances, such as cocaine. Cocaine is a powerful stimulant whereas ethanol is generally considered to be a depressant, with some stimulating properties. The subjective effects of these two substances in a dependent individual may often appear to be more similar than they are different. Animals also self-administer both substances. Basically, although both substances have anesthetic properties and both act to functionally increase catecholaminergic function, especially that of dopamine, there are some differences in their actions. Both alcohol and cocaine have various effects on several neurotransmitters and systems, which ultimately interact to produce the feeling of well-being avidly sought by many individuals today. This drive often eventually produces a dependence which has associated social and medical consequences. It seems likely that the neurochemical changes that ensue following abuse of these substances underlie the phenomena of dependence, tolerance, and subsequent withdrawal. The apparent similarities and differences between these two substances will be reviewed in this chapter.

The molecular biology of addictive drugs

The additive drugs alcohol, morphine, cocaine, and amphetamine are each associated with the development of tolerance and physical dependence. Changes in gene expression occur in cell culture and in vivo with the administration of these centrally-acting drugs. This article reviews those experiments that have studied drug-induced alterations in gene transcription. Ethanol has diverse effects on the amounts of messenger RNA molecules within the central nervous system. Ion channels, neuropeptides, membrane receptors, and immediate early genes represent several regulated mRNAs. The effects are selective, however, as many other specific products are not altered. Evidence for a genetic predisposition to ethanol use reinforces the importance of the genotype. Opioids, cocaine, and amphetamine also affect gene transcription. Messenger RNAs studied have included many of those demonstrated to be altered by alcohol use. Interestingly, use of any of these drugs alters the expression of immediate early genes. These genes may represent an initial step in the pathway that leads to drug addiction. The composite of drug-induced changes in gene expression results in the cellular responses of tolerance and dependence. The characterization of these changes should provide a better understanding of the molecular mechanisms of drug addiction.

Chronic ethanol administration impairs receptor-mediated endocytosis of epidermal growth factor by rat hepatocytes

The effects of chronic ethanol administration on the receptor-mediated endocytosis of epidermal growth factor were studied in isolated rat hepatocytes. In initial experiments, it was demonstrated that significantly less ligand was bound by hepatocytes isolated from rats fed an ethanol liquid diet for 5 to 7 wk than by cells isolated from chow-fed or pair-fed controls. Reduced binding was shown to be primarily caused by a decreased number of surface receptors rather than by changes in receptor affinity. When hepatocytes were incubated at 37 degrees C in the presence of a large saturating concentration of epidermal growth factor (80 nmol/L), intracellular levels of the ligand were significantly lower in cells from the ethanol-fed animals. However, no effect on degradation of the ligand was observed under those conditions. A defect in the initial stages of receptor-ligand internalization was also indicated because less surface-bound ligand was internalized and subsequently degraded in cells from the ethanol-treated rats. When the endocytosis of a lower, more physiological concentration of the growth factor (0.5 nmol/L) was studied, both the uptake of ligand and its degradation were markedly impaired in hepatocytes from the ethanol-fed animals. These results indicate that chronic ethanol administration impairs the receptor-mediated endocytosis of epidermal growth factor by the liver. The major impairment appears to be a reduction of cell surface receptors; however, other steps of the endocytotic pathway also appear to be affected. These altered steps include defective receptor-ligand internalization and changes in intracellular processing of the ligand leading to decreased degradation.