Identification of glyoxylate cycle enzymes in chick liver—the effect of vitamin D₃: Cytochemistry and biochemistry

Abstract

Information regarding the presence of the glyoxylate cycle in chick liver was sought. This metabolic pathway has long been thought to be absent from vertebrate tissues. Previous studies in other tissues have shown that, when present, this pathway is sensitive to vitamin-D. Thus, the effect of long-term vitamin-D deficiency and subsequent vitamin-D replacement on liver structure was studied by light microscopy. In addition, specific biochemical assays for the presence of glyoxylate cycle enzymes were performed. Light microscopy of lipid extracted tissues, light microscopic histochemistry, and quantitative histochemistry showed that the hepatocytes from vitamin-D-deficient animals contained primarily lipid. Hepatocytes from normal and vitamin-D-replete livers contained primarily carbohydrate as judged by their staining with periodic acid-Schiff (PAS). Also, malate synthase positive peroxisomes were seen in hepatocytes from normal and vitamin-D-treated chicks. Structures positive for this glyoxylate cycle enzyme were rarely seen in the hepatocytes from vitamin-D-deficient animals. Biochemical analyses showed the presence of the two unique glyoxylate cycle enzymes, isocitrate lyase and malate synthase, in chick hepatocytes. The activity of these enzymes was markedly increased in the vitamin-D-replete livers. In addition, chick hepatocytes demonstrated the capacity to oxidize fatty acid in the presence of cyanide. This activity, which is characteristic of peroxisomal B-oxidation rather than mitochondrial, was stimulated by vitamin-D treatment. Lastly, incubation of chick liver in the presence of a fatty acid substrate (palmitate) led to higher tissue glycogen content. The latter was further increased in liver from vitamin-D-replete animals. These data show the presence of glyoxylate cycle enzymes in a higher vertebrate and indicate that this tissue is endowed with the capacity to convert lipid to carbohydrate.

Modulation of the peroxisomal gene expression pattern by dehydroepiandrosterone and vitamin D: therapeutic implications

“…The difference in expression level is difficult to interpret and might be due to either stimulation at a higher single dose of propylene glycol, or downregulation by a repeated exposure to a lower dose, or vice versa; the total dose administered in both cases being nearly the same. With a single dose of propylene glycol no effect was found on peroxisomal -oxidation activity, or on malate synthase or isocitrate lyase activities in chick liver homogenates as compared with the control not receiving propylene glycol (Davis et al 1990). On cytosolic and microsomal enzyme activities also, some effects of propylene glycol were reported by Yamamoto & Adachi (1978).…”

“…Further indication for a possible role of VD in the regulation of the peroxisomal compartment is provided by studies that demonstrated peroxisome proliferation in chicken liver (Davis et al 1990) and gut epithelium (Davis & Jones 1984) in response to VD. The same authors have demonstrated induction by VD of peroxisomal -oxidation in rat liver (Davis et al 1989).…”

Induction of glyoxylate cycle enzymes in rat liver upon food starvation

“…4). In the present investigation the key enzymes of the glyoxylate cycle, isocitrate lyase and malate synthase, have been demonstrated in liver extracts of food-starved rats. To date, there has only been scarce evidence for the glyoxylate cycle in animals, except in larvae of lower invertebrates in which it serves for utilization of stored fats for gluconeogenesis during growth [14], in some detailed instances in vertebrates [4,5], and in cartilage tissue of the epiphyseal growth plate of rats [6]. The reason for the present finding was that we used starved rats and analyzed these enzymes in liver tissues.…”

“…Glyoxylate cycle activities have also been discovered in some animal tissues such as larvae of nematodes, urinary bladder epithelium cell layer of Buffus marinus [4], and liver of chicken which, after suffering from vitamin D deficiency, was replenished with vitamin D [5]. In mammals, glyoxylate cycle activities have only been found in cartilage tissue of the epiphyseal growth plate of rats [6].…”

Major roles of isocitrate lyase and malate synthase in bacterial and fungal pathogenesis

“…The presence of this metabolic pathway in animals is controversial. ICL and MS activities have been reported in birds and amphibians (Davis et al, 1986(Davis et al, , 1990) and a recent comparative genomic study showed the presence of an ICL gene in nematodes and cnidaria and an MS gene in nematodes, cnidaria, echinoderms, amphibians, fish, and insects. Interestingly, in placental mammals the MS gene is a pseudogene and the ICL gene is absent (Kondrashov et al, 2006).…”