Topical aspirin provides protection against galactosemic cataract

SK Gupta; S Joshi; R Tandon; P Mathur

ORIGINAL ARTICLE

Year : 1997 | Volume : 45 | Issue : 4 | Page : 221-225

Topical aspirin provides protection against galactosemic cataract

SK Gupta, S Joshi, R Tandon, P Mathur
Department of Pharmacology, All Institute of Medical Sciences, New Delhi, India

Correspondence Address:
S K Gupta
Department of Pharmacology, All Institute of Medical Sciences, New Delhi
India

Source of Support: None, Conflict of Interest: None

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PMID: 9567017

Abstract

Effect of twice daily administration of aspirin eyedrops on the onset and progression of cataract induced by 30% galactose diet was studied. On the 30th day of galactose feeding while all control group rats showed complete stage IV opacity, those receiving aspirin eyedrops showed only mild cataractous changes of stage I. In vitro studies showed that addition of aspirin to the medium significantly decreased dulcitol formation (p < 0.01) and maintained glutathione levels (p < 0.02). Intraocular penetration studies using isolated goat cornea showed excellent penetration by salicylate indicating feasibility of topical administration. The results of the present study demonstrate that topical aspirin possesses significant anticataract activity in galactosemic cataract.

Keywords: Cataract, galactose, topical aspirin, dulcitol, glutathione, corneal penetration

How to cite this article:
Gupta S K, Joshi S, Tandon R, Mathur P. Topical aspirin provides protection against galactosemic cataract. Indian J Ophthalmol 1997;45:221-5

How to cite this URL:
Gupta S K, Joshi S, Tandon R, Mathur P. Topical aspirin provides protection against galactosemic cataract. Indian J Ophthalmol [serial online] 1997 [cited 2023 Jun 5];45:221-5. Available from: https://journals.lww.com/ijo/pages/default.aspx/text.asp?1997/45/4/221/14997

The first indication that non-steroidal anti-inflammatory drugs (NSAIDs) could provide protection against cataract came from epidemiological studies which showed that the population of rheumatoid arthritis patients regularly consuming these drugs had significantly lower incidence of cataract.[1] Patients of cardiovascular disease prescribed aspirin also showed a similar decrease in the incidence of cataract.[2] Since then, many attempts have been made to elucidate the possible mechanisms of action of these drugs and also to develop more potent compounds in more suitable dosage forms.

Paracetamol and ibuprofen were effective in delaying cataract formation in diabetic rats.[3] Sulindac and naproxen also demonstrated significant anticataract activity in the galactosemic model of cataractogenesis both by oral and topical routes.[4][5][6][7] Recent studies with NSAIDs indicate that they also possess antioxidant property.[8]

Aspirin by the oral route delayed cataractogenesis in naphthalene dosed rabbits, diabetic and galactose-fed rats.[3],[9] Aspirin acetylates proteins and protects them from attack by cyanate, sugars and steroids all of which may lead to cataract.[3] Aspirin feeding decreased glycation induced aggregation and thiol oxidation of lens proteins.[10]

Any anticataract drug, to ensure least side effects and better patient compliance, should be available as a topical preparation. With this factor in mind, the present study was carried out to investigate the anticataract activity of aspirin in the form of eye-drops and to gain a better understanding of its mechanism of action.

Materials and Methods

Morphological changes in the lens were examined using slitlamp biomicroscopy. Soluble aspirin (aspirin DL lysine) was used as 0.3% eye drops prepared in a 0.3% liquifilm base of hydroxy propyl methyl cellulose.

Experimental induction of cataract in rats

Fifty Wistar rats, each weighing 50 ± 5 (mean ± standard deviation) gm were used. There were 25 rats in the control group and 25 in the aspirin group. Rats in both the groups were given a 30% galactose diet and water ad libitum. Four days prior to start of galactose diet, 0.3% aspirin drops were instilled two times a day in both the eyes in rats of aspirin group and continued till the end of the experiment. In control group, vehicle drops were instilled similarly. During application, eyes were kept open for 30 seconds to ensure proper medication without spilling over.

Food and water intake were monitored and rats were weighed once every week. Eyes were examined twice a week by two independent observers using slit lamp after pupil dilation with 1% tropicamide. The stages of cataract were graded according to Sippel's classification.[11] Briefly, lenses similar to those of normal rats were graded as Stage 0; with faint peripheral opacity as stage I; irregular peripheral opacity with slight involvement of the lens in the centre as stage II; lenses with irregular opacity involving entire lens as stage III; and lenses with pronounced opacity readily visible as white spots as Stage IV [Figure - 1]. Number of eyes in control and treatment group showing onset on a particular day and the rate of the progression of cataract were considered as indices of cataract.

Ocular kinetic studies

In vitro kinetic studies were conducted to study the penetration by salicylate across the freshly dissected goat cornea fixed in a special corneal transport model fabricated at the Central Workshop of our institute. A solution containing 1,000 μgm of sodium salicylate in a volume of 100 μl was instilled onto the outer surface of the cornea using a micropipette. A continous flow of Krebs Ringer phosphate solution was maintained in the chamber below the cornea using a slow infusion pump. Fractions were collected from this lower chamber at 30 min intervals and amount of salicylate present was determined by reacting with ferric chloride and reading absorbance at 540 ran by the method of Driver et al.[12] The experiment was repeated using 5 freshly dissected goat corneas and average values for amount of drug crossed at 30 min intervals were calculated.

Lens incubation studies

An attempt was made to understand the mechanism of action of aspirin using isolated lens incubation studies. Glutathione depletion and dulcitol formation in the test and control groups were determined and effect of adding aspirin to the medium was studied. Lens culture studies were carried out using 36 freshly dissected rat lenses. One lens from each rat was taken in the test group while the contralateral lens was taken as the control. Lenses were incubated in TC-199 at 37° C and cataractous challenge was provided by adding 30 mM galactose to the medium. 10 mM aspirin was added to the medium for the test group. Changes in lens glutathione levels were monitored by processing 6 lenses from each group after 2, 4, and 6 hrs of incubation. Similarly, lens dulcitol was determined after 8, 16, and 24 hrs of incubation.

Biochemical estimations

Lens dulcitol was determined by the method of West et al.[13] Briefly acidified lens homogenate was reacted with periodic acid, stannous chloride and chromotropic acid and the absorbance of the purple coloured complex was measured at 570 nm.

Glutathione was estimated by the method of Ellman et al.[14] Lens homogenate was reacted with trichloroacetic acid, phosphate buffer and 5, 5'-dithiobis-(2-nitrobenzoic acid) producing a pale yellow coloured complex which was read spectrophotometrically at 412 nm.

Results

No significant difference in food and water intake or body weight was observed in rats of the two groups.

Protective effect of topical aspirin against galactose induced cataract and its rate of progression are presented in [Figure - 2]. It was observed that on the 5th day of galactose feeding, 100% eyes in the control group were having stage I cataract whereas the onset was significantly delayed in aspirin treated eyes. Only 50% eyes developed stage I cataract while 50% eyes were still normal. Further progression of cataract was much slower in the treatment group as compared to control. It was interesting to note that 29% and 14% eyes were still normal in the aspirin group on the 12th and 21st day of galactose feeding, respectively, and none of the eyes were in stage II on these days. On the 30th day, control rats developed mature cataract while aspirin treated eyes showed no further progression beyond stage I.

Kinetic studies revealed that 65% of the instilled salicylate crossed the goat cornea in 5 hrs and the maximum rate of penetration was observed between 2 and 2.5 hrs after instillation [Figure - 3].

Dulcitol levels in control group lenses were 2.64 ± 0.6 (mean ± standard deviation), 5.48 ± 1.28, and 6.88 ± 0.88 mg/gm after 8, 16, and 24 hrs of incubation, respectively. In contrast, lenses incubated with 10 mM aspirin showed significantly lower dulcitol levels of 1.28 ± 0.2, 2.92 ± 0.24, and 3.72 ± 1.24 mg/gm after incubation for 8, 16 and 24 hrs, respectively [Figure - 4].

Glutathione levels in control group lenses were 2.9 ± 0.2, 1.7 ± 0.1, and 1.1 ± 0.3 μmole/gm after incubation of 2, 4, and 6 hrs, respectively. Addition of aspirin to the medium maintained glutathione levels at 3.2 ± 0.1, 2.75 ± 0.3, and 2.4 ± 0.5 μmole/gm after 2, 4, and 6 hrs of incubation, respectively [Figure - 5].

Discussion

Cataract is a multifactorial disease with many associated risk factors and pathways.[15] Several of these pathways involve changes in lens protein structure due to oxidation, glycation or carbamylation.[4],[16], [17] Evidence from epidemiological, in vitro, and animal studies support the idea that NSAIDs provide protection against cataract.[18], [19] However, different mechanisms have been proposed to explain their anticataract action.

Soluble aspirin has been shown to penetrate ocular tissues and significant levels of aspirin and salicylic acid have been reported in aqueous humor and ocular tissues at 0.5 hrs after instillation.[20], [21] Our kinetic studies confirm that salicylate efficiently crosses the goat cornea and as much as 65% of the applied drug becomes available over 5 hrs. Our results demonstrate that 0.3% aspirin eye drops provide significant protection against sugar induced opacification and further suggest that it has a potential for being used as an anticataract agent. These results become more significant since topical route ensures minimal side effects and better patient compliance.

Galactose induced cataract involves numerous changes in the lens. These include dulcitol formation, glycation of lens proteins, increased hydration, defects in amino-acid transport mechanism, failure of membrane Na-K pump, loss of glutathione, lowering of ATP content, and swelling and vacuole formation.[22] Qin et al have proposed that aspirin prevents binding of galactose to lens proteins by reacting with cysteinyl residues of the lens crystallins.[16]

In-vitro studies with isolated rat lenses in 30 mM galactose medium with and without addition of 10 mM aspirin revealed a significant difference in dulcitol formation in the two groups (after 4 hrs, p<0.01). While average dulcitol level in control lenses was 5 mg/gm, aspirin treated lenses had accumulated only 2.64 mg/ gm of dulcitol. Similar results in this model have been obtained earlier with topical sulindac.[6],[7] These results were explained by the authors on the basis of the ability of NSAIDs to inhibit lens aldose reductase. That aspirin inhibits aldose reductase has also been reported by Chang and Gonzalez.[23]

Recently it has been proposed that although there exists a relationship between the aldose reductase inhibiting property and anticataract potency the two are not directly proportional ie besides inhibiting the enzyme some other property is also contributing to the anticataract activity of sulindac and of naproxen.[4],[6],[7] One important feature of galactose induced cataract is an early and precipitous decrease in lens glutathione. Due to this, antioxidant defences of the lens are compromised in galactose induced cataract. In this situation, protein glycation products which are formed in the lens due to high galactose challenge may undergo auto-oxidation. This could result in lipid peroxidation, increased hydration, rupture of lens fibre membranes, leakage of crystallin proteins, and ultimately loss of lens transparency.[24],[25] A similar series of events has been observed in the Emory mouse model of cataract.[26]

Aspirin prevented glutathione depletion in lenses placed in high galactose medium. After 6 hrs, control lenses had GSH (reduced form of glutathione) level of only 1.1 μmole/gm compared to 2.4 μmole/gm in the aspirin treated lenses. Hothersall et al[27] have proposed that in the lens there is a competition between aldose reductase and glutathione reductase for NADPH which is a common co-factor.[25]

It is possible that aspirin, by inhibiting aldose reductase, spares NADPH (reduced form of nicotinamide adenine dinucleotide phosphate) so that regeneration of GSH from oxidised glutathione is favoured. In this way aspirin would improve the antioxidant status of the lens. Antioxidants such as ascorbate, vitamin E, and beta-carotene, are known to provide protection against cataract.[28] Swamy and Abraham proposed that aspirin partly protects lens proteins against thiol oxidation and subsequent protein aggregation.[10] Our findings are consistent with this hypothesis.

To the best of our knowledge this is the first report on the anticataract effect of topical aspirin. Aspirin is a relatively safe, inexpensive, and easily available drug. In the light of our findings and taking into account many earlier reports,[1][2][3],[7][8][9][10],[16], [17,].[20],[21] it is suggested that trials may be conducted to evaluate the effectiveness of topical aspirin in the Indian population.[29] The millions of cataract patients impose a tremendous burden on our economy and at present the only treatment available is surgical extraction of the lens. Any factor which could delay the onset and progression of cataract even by 10 years would reduce the number of cataract operations required by 45% and will go a long way towards solving this widespread national problem.

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