Ophthalmoscopic and morphogenetic changes in rat lens induced by galactose: attenuation by pyruvate

Role of ultraviolet irradiation and oxidative stress in cataract formation-medical prevention by nutritional antioxidants and metabolic agonists

PURPOSE

Cataract is a significant cause of visual disability with relatively high incidence. It has been proposed that such high incidence is related to oxidative stress induced by continued intraocular penetration of light and consequent photochemical generation of reactive oxygen species, such as superoxide and singlet oxygen and their derivatization to other oxidants, such as hydrogen peroxide and hydroxyl radical. The latter two can also interact to generate singlet oxygen by Haber-Weiss reaction. It has been proposed that in addition to the endogenous enzymatic antioxidant enzymes, the process can be inhibited by many nutritional and metabolic oxyradical scavengers, such as ascorbate, vitamin E, pyruvate, and xanthine alkaloids, such as caffeine.

METHODS

Initial verification of the hypothesis has been done primarily by rat and mouse lens organ culture studies under ambient as well as ultraviolet (UV) light irradiation and determining the effect of such irradiation on its physiology in terms of its efficiency of active membrane transport activity and the levels of certain metabolites such as glutathione and adenosine triphosphate as well as in terms of apoptotic cell death. In vivo studies on the possible prevention of oxidative stress and cataract formation have been conducted by administering pyruvate and caffeine orally in drinking water and by their topical application using diabetic and galactosemic animal models.

RESULTS

Photosensitized damage to lens caused by exposure to visible light and UVA has been found to be significantly prevented by ascorbate and pyruvate. Caffeine has been found be effective against UVA and UVB. Oral or topical application of pyruvate has been found to inhibit the formation of cataracts induced by diabetes and galactosemia. Caffeine has also been found to inhibit cataract induced by sodium selenite and high levels of galactose. Studies with diabetes are in progress.

CONCLUSIONS

Various in vitro and in vivo studies summarized in this review strongly support the hypothesis that light penetration into the eye is a significant contributory factor in the genesis of cataracts. The major effect is through photochemical generation of reactive oxygen species and consequent oxidative stress to the tissue. The results demonstrate that this can be averted by the use of various antioxidants administered preferably by topical route. That they will be so effective is strongly suggested by the effectiveness of pyruvate and caffeine administered topically to diabetic and galactosemic animals.

Evidence of cataplerosis in a patient with neonatal classical galactosemia presenting as citrin deficiency

Classical galactosemia is an autosomal recessive disorder caused by a deficiency of the enzyme galactose-1-phosphate uridyltransferase. Undoubtedly, some of the short term complications are linked to the toxic effects of the accumulated abnormal metabolites (galactose-1-phosphate and galactitol). However, the physiopathology of neonatal liver failure remains unclear. We report the case of a 7-week-old girl who was first diagnosed with liver failure, hypoprotidaemia, ascites and generalized edemas. High citrulline (293 micromol/L), on initial plasma amino acid, suggested the diagnosis of citrin deficiency. As the citric acid cycle intermediates were non-detectable (oxoglutarate, succinate and citrate), a cataplerotic state was suspected. As a result, citrate (as an anaplerotic treatment) induced a clear improvement in her liver function. Four weeks later, this patient was switched to a galactose-free formula (as recommended in citrin deficiency with galactosemia) and her pathological status returned to normal. Citrin deficiency was later ruled out by molecular biology studies; then we reintroduced a galactose-containing formula which re-evoked rapidly vomiting, galactose aversion and hepatic cytolysis and the diagnosis of classical galactosemia was established. Our case clearly shows that cataplerosis could play a role in the pathophysiology of the neonatal liver disease observed in classical galactosemia.

Ethyl pyruvate: a novel anti-inflammatory agent

Ethyl pyruvate (EP) is a simple derivative of the endogenous metabolite, pyruvic acid. Treatment with EP has been shown to improve survival and/or ameliorate organ dysfunction in a wide variety of preclinical models of critical illnesses, such as severe sepsis, acute respiratory distress syndrome, acute pancreatitis and stroke. EP was originally regarded as simply a way to administer pyruvate anion, whilst avoiding some of the problems associated with the instability of pyruvate in aqueous solutions. Increasingly, however, it is becoming apparent that certain pyruvate esters, including EP, have pharmacological effects, such as suppression of inflammation, that are quite distinct from those exerted by pyruvate anion. EP has been tested in human volunteers and shown to be safe at clinically relevant doses. It remains to be determined whether EP can be used successfully to treat human diseases.

The relation between d-galactose injection and mitochondrial DNA 4834bp deletion mutation

Since,D-galactose (D-gal) overload model has been used as a premature aging model, we hypothesized that it may also lead to accelerated aging in the inner ear. Furthermore, though the mitochondrial DNA (mtDNA) 4834 bp deletion mutation has been considered as the marker of aging, there is no information available in the literature concerning the mtDNA 4834 bp deletion mutation condition of the D-gal induced premature aging model. We investigate the changes in inner ear enzymatic activity, the occurring of mtDNA 4834 bp deletion in inner ear and other tissues and the relating hearing thresholds after the administration of high dosage (150 mg/kg per day) and low dosage (50 mg/kg per day) of D-gal to rats. Furthermore, the incidence of the mtDNA 4834 bp deletion in different tissues as well as in blood sample was compared. The results showed that daily subcutaneous injections of D-gal into rats for 8 weeks could lead to the biochemical defects and mtDNA 4834 bp deletion in the inner ear tissue and other tissues, which represent the typical aging animals, but the relating hearing threshold shifts (TS) were nearly identical in the three groups. This study also indicates that using of blood samples to detect mtDNA 4834 bp deletion in clinical research might lead to a 'false negative' result. A higher sensitive result could be gained using tissue biopsy to examine mtDNA 4834 bp deletion.