Smoking specifically induces metallothionein-2 isoform in human placenta at term.
Recently, we reported the presence of higher levels of metallothionein (MT) in placentas of smokers compared to non-smokers. In the present study, we designed experiments to separate and evaluate two isoforms of MT (MT-1 and MT-2) in placentas of smokers and non-smokers. Metallothionein was extracted and separated by ion-exchange high performance liquid chromatography (HPLC), previous saturation with cadmium chloride. Two peaks eluting at 6 and 12.5 min, corresponding to MT-1 and MT-2, respectively, were obtained. Metallothionein present in both peaks was identified by Western blot analysis using a monoclonal antibody directed against MT-1 and MT-2. Each isoform concentration was calculated after measuring its cadmium content by atomic absorption spectrometry with inductively coupled-plasma. In placentas of smokers, MT-2 levels increased by seven-fold compared to non-smokers, whereas MT-1 was not changed. Total placental cadmium and zinc concentrations, determined by atomic absorption spectrometry and neutron activation analysis, respectively, were higher in smokers. Metallothioneins levels were clearly in excess to bind all cadmium ions present in placentas. However, most of placental zinc remains unbound to MTs, although as much as twice zinc ions could be bound to MT in smokers. In conclusion, MT-2 is the main isoform induced by smoking, suggesting that this isoform could be involved in placental cadmium and zinc retention. This fact, which could contribute to reduce the transference of zinc to the fetus, may be associated to detrimental effects on fetal growth and development.
Ronco
Ana Maria
AM
Laboratorio de Hormonas y Receptores, Instituto de Nutrición y Tecnología de los Alimentos, INTA, Universidad de Chile, Casilla 138-11, El Libano 5524, Macul, Santiago, Chile. amronco@inta.cl
Garrido
Fernando
F
Llanos
Miguel N
MN
D015153:Blotting, Western; D002104:Cadmium / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003367:Cotinine / Q000652:urine; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008431:Maternal-Fetal Exchange; D008668:Metallothionein / Q000378:metabolism*; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D020033:Protein Isoforms; D012907:Smoking / Q000009:adverse effects / Q000378:metabolism* / Q000652:urine; D015032:Zinc / Q000378:metabolism
D020033:Protein Isoforms; D002104:Cadmium; D008668:Metallothionein; D015032:Zinc; D003367:Cotinine