Exercise is the primary factor associated with Hsp70 induction in muscle of treadmill running rats

AIM

The cytoprotective, inducible stress protein, Hsp70, increases in muscles of rodents subjected to strenuous treadmill running. Most treadmill running protocols employ negative reinforcement to encourage animals to exercise. As these stimuli may themselves activate stress responses, the present investigation was conducted to determine their contribution to the exercise-induced expression of Hsp70.

METHODS

Twenty-one male Sprague-Dawley rats were randomly divided into three equal groups including an exercise group (EX), which ran on a treadmill at 30 m min(-1) for 60 min; a stimulation group (STIM), which was not allowed to run, but was stimulated with compressed air and mild electric shock concurrently with their exercising cohort; and a control group (CON), which was housed in the treadmill room during the exercise period. Animals were killed 24 h post-experiment and hearts (H), soleii (SOL) and white gastrocnemii (WG) were harvested and analysed for Hsp70 content (mean% +/- SEM of standard).

RESULTS

Significant increases in Hsp70 (as a % of standard) were noted in H and WG (H = 77.4 +/- 8.5; WG = 93.9 +/- 18.4) of EX but not in STIM (H = 32.5 +/- 4.6; WG = 32.0 +/- 3.4) or CON (H = 20.5 +/- 3.7; WG = 32.4 +/- 7.4). In SOL, Hsp70 expression in EX (126.7 +/- 6.2) was different from STIM (98.3 +/- 10.9) only. This occurred, despite the fact that all groups were exposed to a stressful environment and exhibited elevated (P < 0.001) temperatures (EX -41.2 +/- 0.1 degrees C > STIM -40.5 +/- 0.2 degrees C > CON -39.0 +/- 0.1 degrees C) indicative of a general stress response.

CONCLUSIONS

These data suggest that exercise per se, rather than environmental conditions or noxious stimuli, are responsible for the induction of Hsp70 in rat muscle during treadmill running.

Modelling cortical cataractogenesis XXIV: uptake by the lens of glutathione injected into the rat

PURPOSE

Work of several groups including ours has shown that injection of glutathione may help to prevent the formation of cataract in the rat lens both in vitro and in vivo. These experiments were initiated to investigate the mechanism by which injected glutathione reaches the lens in vivo. The route is uncertain, but might involve either aqueous or vitreous humors, in contact with the lens anterior and posterior, respectively. Kannan's work has indicated that glutathione can be taken up ex vivo from the aqueous, by perfused isolated lens, but has not investigated; (1) whole animal glutathione injections, (2) the relative proportion of reduced and oxidized glutathione, and (3) the possibility that uptake can occur from the vitreous (in contrast to the aqueous humor) route.

METHODS

3H- or 35S-glutathione was injected into rats intraperitoneally and the radioactivity in serum and lens homogenates followed.

RESULTS

The 3H-radioactivity reached a peak in the serum approximately 20-30 min after injection. Counts were also found in the lens, aqueous and vitreous humors. HPLC using a C18 Bondapak column (37 x 300 mm) indicated that the majority of the 3H-radioactivity in the lens was found in a component of a lower molecular weight than glutathione, but 8.1% of the counts occurred in the peak corresponding to reduced glutathione. Analysis of the unidentified radioactive component revealed a mobility the same as that of a dipeptide. Further analysis suggested this contained the amino acids cysteine and glycine bound in peptide linkage. These results suggest that glutathione may be degraded by the gamma-glutamyl cycle, and the action of transpeptidase produced cysteinylglycine. To confirm these results, similar experiments were undertaken using 35S-glutathione injection, to test whether a differently labelled form would be able to enter the lens. Homogenates prepared from the lens 20 min after 35S-glutathione injection were fractionated by HPLC. The glutathione peak contained 4.5% of the radioactivity in the lens extract. This amount was similar in quantity to the value for 3H-glutathione uptake by the lens. The average of the two values indicated that 6.3% of the total lens label was glutathione. The source of the labelled glutathione taken up by the lens was investigated by determining its concentration in the aqueous and vitreous humors and serum. The dipeptide appeared to be the major radiolabelled form occurring in the serum. This may explain its high level in the lens, as a result of uptake from other sources. Analysis using HPLC revealed that reduced glutathione (GSH) was the predominant chemical species of glutathione in the aqueous humor. In the vitreous humor, oxidized glutathione (GSSG) was the major species. The ratio of GSSG:GSH in the vitreous varied between 2:1 and 4:1.

CONCLUSIONS

Over a 4 h period the lens could obtain 12.3% of its total GSH from the injected GSH, using the specific activity of the labelled glutathione to calculate the actual uptake of glutathione by the lens, suggesting a half-time of 16.25 h for replenishing GSH from external sources. The probable route of glutathione entry was by blood plasma and aqueous since the specific activity of the vitreous humor was too low for the vitreous to be a possible source of the lens GSH.

Modelling cortical cataractogenesis 21: in diabetic rat lenses taurine supplementation partially reduces damage resulting from osmotic compensation leading to osmolyte loss and antioxidant depletion

The concentration of taurine and the amino acids, glutathione, cysteine, ascorbate and ATP were determined in the lenses of rats made diabetic with streptozotocin. In the clear lenses, prior to vacuole formation after 1 or 2 weeks of diabetes, the increase in concentration of sorbitol and the total decrease of all these osmolytes were not significantly different. The major components of the osmolytes lost were taurine and amino acids, which together accounted for over 75% of the total osmolyte loss. Since glutathione, ascorbate, taurine and cysteine have been reported to have antioxidant activity, it appears that their loss may potentiate damage occurring as a result of free radicals generated by nonenzymic glycation by the Maillard reaction. Amino acids also lost as a result of the osmotic compensation, are estimated to be responsible for almost half of the antioxidant activity lost. To test this hypothesis, normal and streptozotocin diabetic female Wistar rats were given taurine at 0.05% or 0.10% (w/w) in the diet. This treatment resulted in small only marginally significant increases in serum taurine levels. At the end of 6 weeks the rats were examined for weight gain or loss and at the time of killing, blood was collected for measurement of serum glucose. gamma-Crystallin levels were determined in vitreous and aqueous humours using a radioimmunoassay. A lens from each rat was homogenized in 8 m guanidinium chloride for adenosine triphosphate (ATP) analysis. In normal rats, a small amount of gamma-crystallin was found in the vitreous humour, and an even smaller amount in the aqueous humour. Diabetes caused a 4- to 5-fold increase in the vitreous humour and a 4-fold increase in gamma-crystallin in the aqueous humour. Diabetes also led to a significant worsening in general body condition, loss of body weight, formation of cataracts, and decrease in lens ATP levels. Addition of taurine to the diet of diabetic animals resulted in a significant decrease of gamma-crystallin leakage into the vitreous but not the aqueous humour. Taurine had no effect on the lens ATP levels. Neither streptozotocin diabetes nor taurine in the diet appeared to affect the weight of the lenses.

Cysteine and ascorbate loss in the diabetic rat lens prior to hydration changes

PURPOSE

Glutathione (GSH) loss precedes vacuole formation in the diabetic rat lens, but the cause of this loss is not known. Cysteine availability is a rate limiting factor to glutathione biosynthesis in rat and human lenses but its concentration is not known; therefore free cysteine was measured prior to lens hydration in the diabetic rat lens. GSH can regenerate ascorbate from dehydroascorbate within the lens and potentially modulate the ascorbate pool; therefore ascorbate loss is also a possibility that has not been examined previously.

METHODS

Diabetes was induced in Wistar rats to provide a slowly progressing model of cortical cataract. Age-matched control rats were injected with buffer vehicle only. Lens condition was monitored by binocular slit-lamp microscope after pupil dilation. Lens cysteine and glutathione were measured in the same lens, while ascorbate and total ascorbate (ascorbate + dehydroascorbate) of the contralateral lens were quantified by high performance liquid chromatography electrochemical detection. The 1- and 2-week periods of diabetes were chosen as they both preceded lens hydration changes and Na+/K+ changes, to avoid leakage due to ruptured cell membranes.

RESULTS

Lens weights were not significantly different compared to controls at either the 1- or 2-week periods, and lenses were completely free of initial vacuole formation. Lens GSH concentration was diminished by 72% compared with controls after 1 week of diabetes and 74% after 2 weeks of diabetes. Lens free cysteine was decreased by 62% and 78% compared with controls after 1 and 2 weeks of diabetes, respectively. Total lens ascorbate concentration was decreased by 34% after 1 week of diabetes and 48% after 2 weeks of diabetes. Dehydroascorbate levels represented less than 10% of the total lens ascorbate pool in all experimental groups. GSH and ascorbate concentration were correlated after 1 week of diabetes (p < 0.005) and after 2 weeks of diabetes (p < 0.001). GSH and cysteine concentration were also correlated after 1 week of diabetes (p < 0.001) and after 2 weeks of diabetes (p < 0.001).

CONCLUSIONS

Decreased free cysteine, in the diabetic rat lens, precedes hydration changes and vacuole formation, contributing to decreased glutathione content. While cysteine was not abundant in the lens, its concentration is greater than previously supposed. The lens ascorbate pool was also diminished prior to lens hydration.

Endogenous superoxide-like species and antioxidant activity in ocular tissues detected by luminol luminescence

A new luminescent method was used to detect the reactive oxygen species in aqueous and vitreous humors and in homogenates of the lens and retina of laboratory rats. Superoxide-like activity per microgram protein increased in all tissues with weight of the rat, a good indicator of animal age. Superoxide dismutase, centrophenoxine, soluble vitamin E (D-alpha-Locopherol (polyethlyene glycol 1000) succinate, and N'-diphenyl-p-phenylenediamine (DPPD) reduced the luminescence. Catalase had no effect. These results are consistent with the detected species being superoxide-like.

A new technique for enhancing luminol luminescent detection of free radicals and reactive oxygen species

A novel technique is reported which makes use of (1) an improved method for solubilizing luminol at neutral pH along with (2) the addition of dimethyl sulfoxide to stabilize superoxide anion in the solutions in which luminescence is detected. These improvements resulted in (1) very low blank values of luminescence and (2) an approximately 6-fold increase in sensitivity of detection of peroxide and superoxide, as well as stabilizing the superoxide radical anion. The technique can also be used to evaluate the availability of antioxidants in biological homogenates and fluids.

Modelling cortical cataractogenesis. 13. Early effects on lens ATP/ADP and glutathione in the streptozotocin rat model of the diabetic cataract

A possible contribution to cell toxicity in the diabetic lens due to early ATP loss is not well characterized prior to the appearance of vacuoles in the lens. Changes in lens ATP levels at longer periods of hyperglycaemia (6-8 weeks) have been reported. We used [31P]NMR analysis of lens extracts at three time periods, comparing diabetic to concurrent control groups at 1, 2 and 4 weeks of hyperglycaemia. With this design, significant alterations (> 10%) in the ATP/ADP ratio can be monitored. NMR analysis revealed a decreased ATP/ADP ratio at all time periods, averaging a 38% decrease. Luminescent determination of ATP levels indicates that this decrease is mainly caused by a decrease of 25% in ATP concentration. The early loss of GSH was large and not accompanied by an appearance of GSSG, as monitored by HPLC electrochemical detection. A 1-week experiment with animals receiving daily insulin treatment was carried out to control for effects of STZ on the lens. This treatment resulted in normal lens GSH levels and a near normal [31P]NMR profile.

Modelling cortical cataractogenesis. XI. Vitamin C reduces gamma-crystallin leakage from lenses in diabetic rats

Normal and streptozotocin diabetic female Wistar rats were given vitamin C (VC) at 0.3% or 1.0% (w/w) in the diet: 1% dietary VC resulted, in 12-24 hr, in significant increases in serum ascorbate levels and lens ascorbate concentrations in normal rats. The increase was biphasic, with VC concentrations falling to a lower level which was still significantly elevated compared to controls in the period of 1.7-4 days for serum and 1.7-5 days for lenticular VC. At the end of 10 weeks the rats were examined for weight gain or loss, general body condition and cataracts. At the time of killing, blood was collected for measurement of serum glucose. Alpha-crystallin levels were determined in vitreous and aqueous humours using a radioimmunoassay. One lens from each rat was fixed for either scanning electron microscopy or light microscopy; the other lens was homogenized in 8 M guanidinium chloride for adenosine triphosphate analysis. In normal rats, a small amount of gamma-crystallin was found in the vitreous humour, and an even smaller amount in the aqueous humour. Diabetes caused a five-fold increase in the vitreous humour and a 2.5-fold increase in gamma-crystallin in the aqueous humour. Diabetes also led to a significant worsening in general body condition, loss of body weight, formation of cataracts, and decrease in lens adenosine triphosphate levels. Addition of VC to the diet of diabetic animals resulted in reduction in cataracts and a decrease of gamma-crystallin leakage into the aqueous and vitreous humours. VC had no effect on lens adenosine triphosphate levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Modeling cortical cataractogenesis: IX. Activity of vitamin E and esters in preventing cataracts and gamma-crystallin leakage from lenses in diabetic rats

Normal and streptozotocin diabetic female Wistar rats were given vitamin E in the diet as the tocopherol, acetate, or succinate form (2,850 IU/kg food). At the end of 6 weeks, the rats were examined for weight gain or loss, general body condition, and cataracts. At sacrifice, blood was collected for measurement of serum glucose, and gamma-crystallin levels were measured in aqueous and vitreous humors using a radioimmunoassay. One lens was homogenized in 8 M guanidinium chloride for ATP analysis. In normal rats, gamma-crystallin was detected in both aqueous and vitreous humors, with the higher concentration in the vitreous humor. Diabetes caused a sixfold increase in gamma-crystallin in both the aqueous and vitreous humors. Diabetes also led to a significant worsening in general body condition, loss of body weight, formation of cataracts, and decrease in lens ATP levels. Addition of vitamin E and vitamin E succinate, but not vitamin E acetate, to the diet resulted in reduction of gamma-crystallin leakage into the vitreous humors and an increase in body weight. There was no improvement noted for the lens ATP levels, the general body condition, or visual cataract score. Neither streptozotocin-induced diabetes nor vitamin E in the diet appeared to affect the weight of the lenses.

Modelling cortical cataractogenesis VIII: effects of butylated hydroxytoluene (BHT) in reducing protein leakage from lenses in diabetic rats

Normal and streptozotocin diabetic female Wistar rats were given butylated hydroxytoluene at 0-, 0.067- or 0.50% w/w in the diet. At the end of 10 weeks, the animals were examined for weight gain or loss, general body condition, and cataracts. After death, blood was collected for measurement of serum glucose. gamma-Crystallin was determined in aqueous and vitreous humours using a radioimmunoassay. One lens from each rat was homogenized in 8 M guanidinium chloride for adenosine triphosphate analysis. In normal rats, there is a small amount of gamma-crystallin found in the vitreous humour, and an even smaller amount in the aqueous humour. Diabetes caused a 2.5-fold increase of gamma-crystallin in the aqueous humour and a five-fold increase in the vitreous humour. Diabetes also led to a significant worsening in general body condition, loss of body weight, decrease in lens adenosine triphosphate levels, and formation of cataracts. Addition of butylated hydroxytoluene (BHT) to the diet resulted in improved general body condition, reduction in cataracts, decrease of gamma-crystallin leakage into the vitreous humour, and weight gain. There was no effect of dietary butylated hydroxytoluene on levels of lens adenosine triphosphate. Neither the diabetic state nor treatment with butylated hydroxytoluene affected the weight of the lenses.