Galactose Metabolism in Mice with Galactose-1-Phosphate Uridyltransferase Deficiency: Sucklings and 7-Week-Old Animals Fed a High-Galactose Diet

doi:10.1006/mgme.2001.3152

Molecular Genetics and Metabolism

Volume 72, Issue 4, April 2001, Pages 306-315

https://doi.org/10.1006/mgme.2001.3152 Get rights and content

Abstract

Mice deficient in galactose-1-phosphate uridyltransferase (GALT) demonstrate abnormal galactose metabolism but no obvious clinical phenotype. To further dissect the pathways of galactose metabolism in these animals, galactose oxidation and metabolite levels were studied in 16-day-old sucklings and the effect of a 4 week prior exposure to a 40% glucose or 40% galactose diet was determined in 7-week-old mice. Suckling GALT-deficient (G/G) mice slowly oxidized [1-¹⁴C]galactose to ¹⁴CO₂, 4.0% of the dose when fed and 7.9% when fasted compared to normal animals 38.3 and 36.4% in 4 h, respectively. Plasma of G/G sucklings contained 11.1 mM galactose and erythrocyte galactose 1-phosphate levels were 28.2 and 31.9 mg/dl packed cells. Galactose, galactitol, galactonate, and galactose 1-phosphate were found in G/G suckling mouse tissues. The tissue galactose concentrations were 10% or less of that in plasma, suggesting that there was limited cellular entry of galactose. In 7-week-old fasted mice with 4 weeks prior exposure to glucose or galactose-containing diet, 4-h oxidation was 12.9 and 15.0% of the administered radiolabeled galactose, respectively. Normal animals oxidized 33.9 and 37.9% of the dose when fed the same diets, respectively. The ability of G/G mice to oxidize galactose in the absence of GALT activity suggests the presence of alternate metabolic pathways for galactose disposition. G/G mice fed the galactose-free 40% glucose diet had erythrocyte galactose 1-phosphate levels ranging from 6.4 to 17.7 mg/dl packed cells and detectable galactose and galactose metabolites in tissues, suggesting that these animals endogenously produced galactose. The plasma of 40% galactose-fed G/G mice contained 9.1 mM galactose with red blood cell galactose 1-phosphate averaging 43.6 mg/dl. Tissues of these animals also contained high levels of galactose and galactose 1-phosphate. Liver contained over 4 μmol/g galactonate but little galactitol. Despite the elevated galactose and galactose 1-phosphate, the animals tolerated the high-galactose diet and were indistinguishable from normal animals, exhibiting no manifestations of galactose toxicity seen in human GALT-deficient galactosemia. The data suggest that high galactose 1-phosphate levels do not cause galactose toxicity and that high galactitol in combination with galactose 1-phosphate may be a prerequisite. Absence of GALT appears necessary but insufficient to produce human galactosemic phenotype.

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Galactose in human metabolism, glycosylation and congenital metabolic diseases: Time for a closer look
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Citation Excerpt :
The galactonate pathway was first discovered in mammals in 1966 from in vitro studies conducted on healthy rat liver [38]. Later, accumulation of D-galactonate (or D-galactonic acid) was detected also in other tissues, including rat intestine, heart and kidney when rats were maintained on a prolonged high-galactose diet [39–41]. In Guinea pigs high-galactose diet led to accumulation of D-galactono-1,4-lactone in lens, testis, circulation and muscles when galactitol production was suppressed [42,43].
Galactose is an essential carbohydrate for cellular metabolism, as it contributes to energy production and storage in several human tissues while also being a precursor for glycosylation. Galactosylated glycoconjugates, such as glycoproteins, keratan sulfate-containing proteoglycans and glycolipids, exert a plethora of biological functions, including structural support, cellular adhesion, intracellular signaling and many more. The biological relevance of galactose is further entailed by the number of pathogenic conditions consequent to defects in galactosylation and galactose homeostasis. The growing number of rare congenital disorders involving galactose along with its recent therapeutical applications are drawing increasing attention to galactose metabolism.
In this review, we aim to draw a comprehensive overview of the biological functions of galactose in human cells, including its metabolism and its role in glycosylation, and to provide a systematic description of all known congenital metabolic disorders resulting from alterations of its homeostasis.
Partial replacement of glucose by galactose in the post-weaning diet improves parameters of hepatic health
2019, Journal of Nutritional Biochemistry
Replacing part of glucose with galactose in the post-weaning diet beneficially affects later life metabolic health in female mice. The liver is the main site of galactose metabolism, but the direct effects of this dietary intervention on the liver in the post-weaning period are not known. The aim of this study was to elucidate this.
Weanling female mice (C57BL/6JRccHsd) were fed a starch containing diet with glucose (32 en%) monosaccharide (GLU), or a diet with glucose and galactose (1:1 both 16 en%) (GLU+GAL). Body weight, body composition, and food intake were determined weekly. After 3 weeks, mice were sacrificed, and serum and liver tissues were collected. Global hepatic mRNA expression was analyzed and hepatic triglyceride (TG) and glycogen contents were determined by enzymatic assays.
Body weight and body composition were similar in both groups, despite higher food intake in mice on GLU+GAL diet. Hepatic TG content was lower in GLU+GAL-fed than GLU-fed females, while glycogen levels were unaffected. Analysis of global expression patterns of hepatic mRNA showed that mainly inflammation-related pathways were affected by the diet, which were predominantly downregulated in GLU+GAL-fed females compared to GLU-fed females. This reduction in inflammation in GLU+GAL-fed females was also reflected by decreased serum concentrations of acute phase protein Serum amyloid A 3.
In conclusion, replacing part of glucose with galactose in the post-weaning diet reduces hepatic TG content and hepatic inflammation.
Alterations of galactose metabolism caused by deficit of galactose-1-phosphate uridylyltransferase activity: An overview of galactosemia type I
2019, Molecular Nutrition Carbohydrates
Galactosemia type I is caused by a deficiency of the galactose-1-phosphate uridylyltransferase enzyme, encoding by the GALT gene. This pathology is inherited in an autosomal recessive pattern. Following galactose intake by galactosemic neonates, a toxic buildup of galactose metabolism intermediates is produced. Promptly, various signs appeared such as lethargy, poor feeding, jaundice, and hepatomegaly. Treatment is relatively easy to achieve to prevent acute symptoms and save the baby's life. However, even when patients undergo lifelong galactose dietary restrictions, some subjects develop mild to severe long-term complications. The mutational spectrum is characterized by allele heterogeneity, where few alleles have high frequency and a clear ethnic distribution. Missense mutations are the most common variants and are distributed along the whole GALT gene, altering functional and structural features of the enzyme. Dietary treatments consist of eliminating lactose- and galactose-rich foods and supplying formulas of soy milk. This diet should be maintained through the whole life of the patient. In contrast, the diet should be absolutely normal in the Duarte form of galactosemia. Experts reached a consensus and recommended the consumption of fruits, vegetables, legumes, unfermented soy products, and hard chesses.
The galactose-induced decrease in phosphate levels leads to toxicity in yeast models of galactosemia
2017, Biochimica et Biophysica Acta - Molecular Basis of Disease
Citation Excerpt :
One of the hallmarks of classic galactosemia is the intracellular accumulation of galactose-1-phosphate. Although there are evidences that not all negative outcomes correlates with galactose-1-phosphate accumulation in patients [6–9] and in other models of classic galactosemia [10,11], it is believed that the accumulation of this metabolite is relevant to the pathophysiology of this disease in a still elusive manner [12]. Galactose-1-phosphate is proposed to act as an inhibitor of a series of enzymatic activities such as phosphoglucomutase, glucose-6-phosphate phosphatase, glucose-6-phosphate dehydrogenase, glycogen phosphorylase, UDP-glucose pyrophosphorylase and inositol monophosphatase [12–14].
Classic galactosemia is an inborn error of metabolism caused by deleterious mutations in the GALT gene. A number of evidences indicate that the galactose-1-phosphate accumulation observed in patient cells is a cause of toxicity in this disease. Nevertheless, the consequent molecular events caused by the galactose-1-phosphate accumulation remain elusive. Here we show that intracellular inorganic phosphate levels decreased when yeast models of classic galactosemia were exposed to galactose. The decrease in phosphate levels is probably due to the trapping of phosphate in the accumulated galactose-1-phosphate since the deletion of the galactokinase encoding gene GAL1 suppressed this phenotype. Galactose-induced phosphate depletion caused an increase in glycogen content, an expected result since glycogen breakdown by the enzyme glycogen phosphorylase is dependent on inorganic phosphate. Accordingly, an increase in intracellular phosphate levels suppressed the galactose effect on glycogen content and conferred galactose tolerance to yeast models of galactosemia. These results support the hypothesis that the galactose-induced decrease in phosphate levels leads to toxicity in galactosemia and opens new possibilities for the development of better treatments for this disease.
The molecular basis of galactosemia — Past, present and future
2016, Gene
Galactosemia, an inborn error of galactose metabolism, was first described in the 1900s by von Ruess. The subsequent 100 years has seen considerable progress in understanding the underlying genetics and biochemistry of this condition. Initial studies concentrated on increasing the understanding of the clinical manifestations of the disease. However, Leloir's discovery of the pathway of galactose catabolism in the 1940s and 1950s enabled other scientists, notably Kalckar, to link the disease to a specific enzymatic step in the pathway. Kalckar's work established that defects in galactose 1-phosphate uridylyltransferase (GALT) were responsible for the majority of cases of galactosemia. However, over the next three decades it became clear that there were two other forms of galactosemia: type II resulting from deficiencies in galactokinase (GALK1) and type III where the affected enzyme is UDP-galactose 4′-epimerase (GALE). From the 1970s, molecular biology approaches were applied to galactosemia. The chromosomal locations and DNA sequences of the three genes were determined. These studies enabled modern biochemical studies. Structures of the proteins have been determined and biochemical studies have shown that enzymatic impairment often results from misfolding and consequent protein instability. Cellular and model organism studies have demonstrated that reduced GALT or GALE activity results in increased oxidative stress. Thus, after a century of progress, it is possible to conceive of improved therapies including drugs to manipulate the pathway to reduce potentially toxic intermediates, antioxidants to reduce the oxidative stress of cells or use of “pharmacological chaperones” to stabilise the affected proteins.
Pediatric Liver Disease and Inherited, Metabolic, and Developmental Disorders of the Pediatric and Adult Liver
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¹: To whom correspondence should be addressed at Research Metabolism, The Children's Hospital of Philadelphia, 402 Abramson Pediatric Research Building, 3516 Civic Center Boulevard, Philadelphia, PA 19104-4318. Fax: (215) 590-3364. E-mail: [email protected].

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Regular ArticleGalactose Metabolism in Mice with Galactose-1-Phosphate Uridyltransferase Deficiency: Sucklings and 7-Week-Old Animals Fed a High-Galactose Diet

Abstract

Biochem Molec Med

Am J Med

J Biol Chem

Clin Chem Acta

Metabolism

J Biol Chem

Exp Eye Res

Lancet

Molec Genet Metab

Disorders of Galactose Metabolism

Galactosemia today. The enigma and the challenge

J Inherit Metab Dis

Galactose metabolism by the mouse with galactose-1-phosphate uridyltransferase deficiency

Pediatr Res

A fluorometric method for assay of galactose-1-phosphate in red blood cells

J Lab Clin Med

In vivo oxidation of 1-13Cgalactose in patients with galactose-1-phosphate uridyltransferase deficiency

Biochem Molec Med

Regular Article
Galactose Metabolism in Mice with Galactose-1-Phosphate Uridyltransferase Deficiency: Sucklings and 7-Week-Old Animals Fed a High-Galactose Diet

In vivo oxidation of 1-¹³Cgalactose in patients with galactose-1-phosphate uridyltransferase deficiency