The alkali burned cornea: electron microscopical, enzyme histochemical, and biochemical observations

Emerging Strategies in Treating Corneal Alkali Burns: A Narrative Review

Corneal alkali burns represent a complex and debilitating ocular injury, necessitating innovative strategies for effective management. This narrative medical review seeks to provide a comprehensive exploration of emerging approaches in the treatment of corneal alkali burns. The primary objectives of this review are multifaceted. First, we aim to unravel the intricate pathophysiology of corneal alkali burns, delving into the immediate and long-term consequences of alkali exposure on ocular tissues. Understanding the underlying mechanisms, including oxidative stress, inflammation, and neovascularization, is essential for the development of targeted therapeutic interventions. Second, we assess the efficacy of novel treatment modalities, encompassing pharmacological agents and surgical techniques, with a focus on their ability to mitigate corneal damage, facilitate tissue regeneration, and preserve visual function. By analyzing the latest clinical findings, we aim to identify promising avenues for improved patient outcomes. Temporal dynamics play a crucial role in the healing process, and thus our review investigates the progression of corneal lymphangiogenesis and the expression patterns of key growth factors, such as vascular endothelial growth factor-C (VEGF-C). These insights into the timing of corneal healing provide valuable guidance for tailoring therapeutic interventions to specific stages of injury. Finally, we delve into regenerative therapies, particularly the potential of mesenchymal stem cells (MSCs) and their secretome as anti-inflammatory and antiangiogenic agents. By summarizing the promising results from preclinical and clinical studies, we illuminate the prospects of regenerative approaches in corneal alkali burn management. This narrative review aspires to serve as an indispensable resource for clinicians, researchers, and healthcare professionals involved in the treatment of corneal alkali burns. By addressing these objectives, we aim to foster a deeper understanding of this challenging condition, facilitate the development of innovative strategies, and ultimately enhance patient outcomes in the realm of corneal health and vision preservation.

Collagen analogs with phosphorylcholine are inflammation-suppressing scaffolds for corneal regeneration from alkali burns in mini-pigs

The long-term survival of biomaterial implants is often hampered by surgery-induced inflammation that can lead to graft failure. Considering that most corneas receiving grafts are either pathological or inflamed before implantation, the risk of rejection is heightened. Here, we show that bioengineered, fully synthetic, and robust corneal implants can be manufactured from a collagen analog (collagen-like peptide-polyethylene glycol hybrid, CLP-PEG) and inflammation-suppressing polymeric 2-methacryloyloxyethyl phosphorylcholine (MPC) when stabilized with the triazine-based crosslinker 4-(4,6-Dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride. The resulting CLP-PEG-MPC implants led to reduced corneal swelling, haze, and neovascularization in comparison to CLP-PEG only implants when grafted into a mini-pig cornea alkali burn model of inflammation over 12 months. Implants incorporating MPC allowed for faster nerve regeneration and recovery of corneal sensation. CLP-PEG-MPC implants appear to be at a more advanced stage of regeneration than the CLP-PEG only implants, as evidenced by the presence of higher amounts of cornea-specific type V collagen, and a corresponding decrease in the presence of extracellular vesicles and exosomes in the corneal stroma, in keeping with the amounts present in healthy, unoperated corneas.

Adipose-derived mesenchymal stromal cells promote corneal wound healing by accelerating the clearance of neutrophils in cornea

The dome-shaped cornea is a transparent, non-vascularized, and epithelialized highly organized tissue. Physical and chemical injuries may trigger corneal wound healing (CWH) response and result in neovascularization that impairs the visual function. CWH involves not only migration, proliferation, and differentiation of the cells in different layers of cornea, but also the mobilization of immune cells. We demonstrated here that human adipose-derived mesenchymal stromal cells (ADSCs) could effectively inhibit neovascularization during ethanol-induced injury in mouse cornea. Importantly, we found that while neutrophils are essential for CWH, excessive and prolonged neutrophil retention during the granulation stage contributes to neovascularization. ADSCs were found to promote the clearance of neutrophils in the cornea during the granulation stage, likely via increasing the reverse transendothelial cell migration of CXCR4high neutrophils from cornea to the lung. Our results demonstrate that ADSCs are effective in treating CWH-induced neovascularization and modulation of neutrophil clearance could be novel strategies for better vision recovery after injury.

Anti-inflammatory and antioxidant effects of Tualang honey in alkali injury on the eyes of rabbits: experimental animal study

BACKGROUND

Alkali injury is one of the most devastating injuries to the eye. It results in permanent unilateral or bilateral visual impairment. Chemical eye injury is accompanied by an increase in the oxidative stress. Anti-inflammatory and antioxidant agents play a major role in the treatment of chemical eye injuries. The purpose of this study is to evaluate the anti-inflammatory (clinical and histopathological) and antioxidant effects of Tualang honey versus conventional treatment in alkali injury on the eyes of rabbits.

METHODS

A preliminary study was carried out prior to the actual study to establish the alkali chemical injury on rabbit's cornea and we found that alkali chemical injury with 2 N NaOH showed severe clinical inflammatory features. In actual study, alkali injury with 2 N NaOH was induced in the right eye of 10 New Zealand White rabbits' cornea. The rabbits were divided into two groups, Group A was given conventional treatment and Group B was treated with both topical and oral Tualang honey. Clinical inflammatory features of the right eye were recorded at 12 hours, 24 hours, 72 hours, 5th day and 7th day post induction of alkali burn on the cornea. The histopathological inflammatory features of the right corneas of all rabbits were also evaluated on day-7. The level of total antioxidant status and lipid peroxidation products in the aqueous humour, vitreous humour and serum at day-7 were estimated biochemically. Fisher's Exact, Chi-Square and Mann-Whitney test were used to analyse the data.

RESULTS

There was no statistically significant difference in clinical inflammatory features (p > 0.05) between honey treated and the conventional treated group at different times of examination. Histopathological examination of the cornea showed the number of polymorphonuclear leucocytes was below 50 for both groups (mild grade). There was also no significant difference in the level of total antioxidant status as well as lipid peroxidation products in aqueous humour (p = 0.117, p = 0.382 respectively), vitreous humour (p = 0.917, p = 0.248 respectively) and serum (p = 0.917, p = 0.332 respectively) between honey treated and the conventional treated group.

CONCLUSION

Tualang honey has almost the equal effects when compared with the conventional treatment in treating alkali injury on rabbit's eye. Future research with more number of rabbits and control group is warranted to explore the anti-inflammatory and antioxidant effects of Tualang honey.

Proteomic analyses of corneal tissue subjected to alkali exposure

PURPOSE

To determine whether exposure to alkaline chemicals results in predictable changes in corneal protein profile. To determine whether protein profile changes are indicative of severity and duration of alkali exposure.

METHODS

Enucleated bovine and porcine (n = 59 each) eyes were used for exposure to sodium, ammonium, and calcium hydroxide, respectively. Eyes were subjected to fluorescein staining, 5-bromo-2'-deoxy-uridine (BrdU) labeling. Excised cornea was subjected to protein extraction, spectrophotometric determination of protein amount, dynamic light scattering and SDS-PAGE profiling, mass spectrometric protein identification, and iTRAQ-labeled quantification. Select identified proteins were subjected to Western blot and immunohistochemical analyses.

RESULTS

Alkali exposure resulted in lower protein extractability from corneal tissue. Elevated aggregate formation was found with strong alkali exposure (sodium hydroxide>ammonium, calcium hydroxide), even with a short duration of exposure compared with controls. The protein yield after exposure varied as a function of postexposure time. Protein profiles changed because of alkali exposure. Concentration and strength of the alkali affected the profile change significantly. Mass spectrometry identified 15 proteins from different bands with relative quantification. Plexin D1 was identified for the first time in the cornea at a protein level that was further confirmed by Western blot and immunohistochemical analyses.

CONCLUSIONS

Exposure to alkaline chemicals results in predictable and reproducible changes in corneal protein profile. Stronger alkali, longer durations, or both, of exposure resulted in lower yields and significant protein profile changes compared with controls.

TIMP-1 role in protection against Pseudomonas aeruginosa-induced corneal destruction

To establish the role of TIMP-1 in protection against Pseudomonas aeruginosa-induced corneal destruction, corneas of adult 8-week-old (resistant) and aged 12-month-old (susceptible) mice were infected with the bacterium. Corneas were analyzed for TIMP-1 protein by immunocytochemistry and Western blotting. Basement membrane (BM) integrity was assessed by immunostaining for type IV collagen. Additionally, resistant 8-week-old mice were treated systemically with neutralizing TIMP-1 polyclonal antibody (pAb) or pre-immune normal rabbit serum (NRS). Ocular and BM integrity as well as MMP-9 expression were examined in these mice. A greater amount of TIMP-1 protein was observed in the cornea of 8-week-old mice. In the cornea, the strongest staining was found in the superficial epithelium, but positive staining also was seen in the basal epithelium and stroma. When type IV collagen was analyzed in the BM of both age groups of mice, a distinct staining pattern was observed in only the young adult mice. Treatment of 8-week-old resistant mice with neutralizing TIMP-1 pAb vs NRS increased the amount of MMP-9 in the cornea of TIMP-1 pAb-treated mice and affected the ability of these mice to deposit BM components. These studies suggest that adequate expression of TIMP-1 protects against BM and stromal degradation via multiple processes.

A physiological perspective on the swelling properties of the mammalian corneal stroma

PURPOSE

The present studies were designed to assess whether measurement of corneal stroma swelling in the laboratory, especially in non-physiological solutions, was associated with a measurable effect on the keratocytes.

METHODS

Complete corneal stroma preparations were made from quality- and age-selected recent post-mortem cattle eyes. These were either assessed immediately or incubated in three different solutions, namely a balanced salts solution with glucose (BSSG), isotonic phosphate buffered saline (PBS) or pure water. Incubations were carried out at 37 degrees C for 9h, and repeated measures of wet mass made so that the rates and extent of swelling could be determined. After incubation, an aqueous extract was made of the stroma for measurements of the levels the enzymes lactate dehydrogenase (LDH), aldehyde dehydrogenase (ALDH) and N-acetyl-beta-glucosaminidase.

RESULTS

The initial rates of swelling were lowest in BSSG, marginally faster in PBS and much faster in water. The secondary rates of swelling showed the same sequence being 10.0%/h in BSSG, 14.8%/h in PBS and 34.2%/h in water. Compared to non-incubated preparations, reductions in all three enzyme activities occurred. For LDH, these were 15% with BSSG, 40% in PBS and 80% with water. Similar results were seen with ALDH activity when comparing the three incubation solutions, while incubation in BSSG also resulted in a substantial (40%) reduction in N-acetyl-glucosaminidase activity.

CONCLUSIONS

When immersed in an isotonic BSSG with added glucose at 37 degrees C, the swelling of a complete bovine corneal stroma is much less than smaller pieces of stroma, and also slightly less than if isotonic PBS was used. With the use of BSSG, little or no change in cytoplasmic enzyme activities occurred, but measurable decreases were noted with PBS and very substantial decreases when water was used, indicating a toxic effect on the keratocytes. The observation that substantial decreases in a lysosomal enzyme activity could occur even with the use of BSSG indicate substantial stress is imposed on the stroma during these types of experiments. Notwithstanding, the data collectively indicate that the keratocyte cells within the collagen matrix of the stroma can be substantially damaged and this needs to be taken into account in future experiments on the true physiology of the corneal stroma.

Synergistic effect with Phe-Gly-Leu-Met-NH2 of the C-terminal of substance P and insulin-like growth factor-1 on epithelial wound healing of rabbit cornea

1. We previously reported that substance P and insulin-like growth factor-1 (IGF-1) synergistically stimulate corneal epithelial wound healing in vitro and in vivo. We wished to identify which portion of the amino acid sequence of substance P might be responsible for this synergism. 2. Corneal epithelial migration was not affected by the addition of any one of the following factors: substance P; Phe-Gly-Leu-Met-NH2 (C-terminal of substance P); Val-Gly-Leu-Met-NH2 (C-terminal of neurokinin A, neurokinin B, and kassinin); Tyr-Gly-Leu-Met-NH2 (C-terminal of physalaemin); Ile-Gly-Leu-Met-NH2 (C-terminal of eledoisin); or Gly-Leu-Met-NH2 (common C-terminal of tachykinins). 3. In the presence of IGF-1, only substance P and Phe-Gly-Leu-Met-NH2 were synergistic in stimulating corneal epithelial migration in a dose-dependent fashion. 4. The combination of Phe-Gly-Leu-Met-NH2 and IGF-1 did not affect the incorporation of [3H]-thymidine into corneal epithelial cells. 5. Treatment with Phe-Gly-Leu-Met-NH2 and IGF-1, but not with Phe-Gly-Leu-Met-NH2 or IGF-1 alone, increased attachment of corneal epithelial cells to a fibronectin matrix. 6. The levels of alpha5 and beta1 integrin were not affected by Phe-Gly-Leu-Met-NH2 or IGF-1 alone, but they were significantly increased by the combination of Phe-Gly-Leu-Met-NH2 and IGF-1. 7. Topical application of the same combination facilitated corneal epithelial wound closure in vivo. 8. These results demonstrated that Phe-Gly-Leu-Met-NH2, a sequence of 4 amino-acids of the C-terminal of substance P, is the minimum sequence necessary to produce the synergistic effects of substance P and IGF-1 on corneal epithelial wound healing.

Topical steroid use in the treatment of ocular alkali burns

BACKGROUND

Ocular alkali burns can be associated with a poor visual outcome. The release of collagenases and proteases after the injury leads to corneoscleral melting. The role of topical steroids in such patients is controversial as they have been postulated to exacerbate corneoscleral melting.

METHODS

30 patients were reviewed retrospectively after admission to King's College Hospital with alkali burns between 1990 and 1993. All patients were treated with an intense and prolonged regimen of topical steroids and topical and systemic vitamin C.

RESULTS

22 patients had mild injuries and eight had severe injuries as estimated by the Roper-Hall grading system. 23 patients were treated with topical steroids for > 10 days and 22 patients were treated with topical vitamin C for more than 10 days. One patient with a severe injury developed corneoscleral melting.

CONCLUSION

Prolonged treatment with topical steroids when used in conjunction with topical vitamin C is not associated with corneoscleral melting.

Hydrolase participation in allograft rejection in rat penetrating keratoplasty

BACKGROUND

A rat model of orthotopic corneal graft rejection was used to investigate the alterations in hydrolase activity within the corneal graft or within cellular infiltrates during acute rejection.

METHODS

The distribution of the lysosomal enzymes [acid phosphatase (AP), N-acetyl-beta-D-glucosaminidase (NAG), beta-glucuronidase (beta-Gluc), beta-galactosidase (beta-Gal), dipeptidylpeptidase II (DPPII)] and of the membrane-bound proteases [aminopeptidase M (APM), aminopeptidase A (APA), gamma-glutamyltransferase (GGT), alkaline phosphatase (ALP), dipeptidylpeptidase IV (DP-PIV)] were investigated by histochemical methods in the grafts at 3, 5, 8, 10 and 12 days following allogeneic transplantation. Serial sections of the grafts were also examined for RT1b, CD4, CD4+, CD8, CD11b/c and CD45, in order to determine hydrolase activity within infiltrating cells.

RESULTS

Allogeneic grafts were invaded by macrophages, CD4- and CD8-positive lymphocytes. In contrast, syngeneic grafts, performed as a control, contained occasional lymphocytes and focal aggregations of macrophages around suture sites. The allogeneic cellular infiltrate stained intensely for AP and ALP; moderately for beta-Gluc, NAG and beta-Gal; and mildly for GGT, DPPII and APM in grafts at all postoperative times. Serial sectioning indicated that the majority of the lysosomal hydrolases were located in macrophages; AP, APM and GGT were, however, observed in lymphocytes. Vessel ingrowth could be observed with enzyme staining for AP, beta-Gluc, NAG, ALP, APA and APM. Hydrolase activity in the corneal endothelium served as an indicator of endothelial function during the rejection process.

CONCLUSION

Changes in normal hydrolase activities in corneal grafts in the rat model indicate decreasing corneal function during the rejection process. Hydrolases released from infiltrating cells contribute to the morphological disruption and, possibly, to graft rejection.

Hydrolases of anterior segment tissues in the normal human, pig and rat eye: a comparative study

The distributions of the hydrolases acid and alkaline phosphatase (AP and ALP), N-acetyl-beta-D-glucosaminidase (NAG), beta-glucuronidase (beta-Gluc), beta-galactosidase (beta-Gal), non-specific esterase (UE), dipeptidylpeptidases II and IV (DPPII and DPPIV), aminopeptidases M and A (APM and APA), and gamma-glutamyltransferase (GGT) were investigated in the human, pig and Lewis rat normal anterior segment by histochemical methods. The distribution of the above hydrolases, particularly that of proteases, varied between ocular tissues and between the three species. Lysosomal hydrolases together with GGT and ALP were consistently active in the corneal epithelium, stroma and endothelium in all three species; the corneal distribution and activity of beta-Gal, APM, APA and DPPIV, however, displayed interspecies variation. The angular tissues showed similarities for most hydrolases with the exceptions of beta-Gal, UE, APM, APA and DPPIV. In all eyes examined strong ciliary epithelial activity for AP, beta-Gal, UE, GGT and ALP was observed in the pars plicata; only the pig eye also displayed strong DPPIV activity in this area. Regional differences in hydrolase distribution in the iris were observed in all species. A post-mortem freezing delay of longer than 24 h resulted in a decrease in hydrolase activity.

Histochemical survey of the anterior segment of the normal human foetal and adult eye

The distributions of the lysosomal enzymes [acid phosphatase (AP), N-acetyl-beta-D-glucosaminidase (NAG), beta-glucuronidase (beta-Gluc), beta-galactosidase (beta-Gal), dipeptidylpeptidase II (DPP II)] and of the membrane-bound proteases [aminopeptidase M (APM), aminopeptidase A (APA), gamma-glutamyltransferase (GGT), dipeptidylpeptidase IV (DPP IV)] were investigated in the normal human adult and foetal anterior segment by histochemical methods. The distribution of these hydrolases varied between ocular tissues. The most active enzymes in the adult corneal epithelium and endothelium were AP, beta-Gluc, NAG, beta-Gal and GGT; in the keratocytes, APM, APA, beta-Gluc and GGT predominated. The adult trabecular meshwork cells were stained by AP, beta-Gluc, NAG, APM, GGT, DPP II and DPP IV. The enzymes AP, beta-Gluc, APM and APA, however, displayed greater activity in the endothelium of Schlemm's canal. The adult ciliary epithelium stained strongly for all lysosomal hydrolases; GGT was the most active protease here. Differences in enzyme activity were noted in some tissues when foetal and adult anterior segments were compared. There appeared to be a decrease in the activity of some enzymes with age and post-mortem delay greater than 24 h. The function(s) of each enzyme and their possible roles in the respective tissues are discussed.

Ascorbic acid phosphate ester and wound healing in rabbit corneal alkali burns: epithelial basement membrane and stroma

We examined the effect of L-ascorbic acid 2-phosphate (P-Asc) on the healing of alkali-burned corneas in rabbits. Round filter paper containing 1 N NaOH was applied to the central cornea for 60 or 120 s to produce the alkali burn. Animals were treated with topical saline, 10% ascorbate, or 6.5% P-Asc applied on the cornea. The corneas were then examined histologically. Burned stroma showed no toluidine blue staining, indicating a loss of glycosaminoglycan. In the 60-s burn group, P-Asc reduced the size of the unstained area as compared with the control. Transmission electron microscopy showed basal lamina under new epithelia in the corneas treated with ascorbate or P-Asc, but not in controls. These observations support the theory that P-Asc may have a therapeutic role in the repair of corneal alkali burns.

Histochemical changes in the rabbit cornea and plasmin activity in the tear fluid during contact lens wear. Favourable influence of protease inhibitors (aprotinin, PC5, elastatinal)

Plasmin activity in the tear fluid of the rabbit eye was examined during the wearing of soft contact lenses (SCL) and compared with the occurrence of corneal disturbances assessed in cryostat sections. Plasmin activity was determined with a semiquantitative method using dry punches of filter paper previously soaked in 0.1 M Tris-HCl buffer solution containing mmol/l D-Val-Leu-Lys-FCA (trifluoromethylaminocoumarine), pH 7.2. Punches were applied to the corneal surface for 5 s (tear collection) and incubated in wet chamber. The time of appearance of the bright yellow fluorescence in UV light was recorded and taken as a measure of plasmin activity. For calibration punches soaked in solutions containing plasmin in various concentrations, and processed in the same manner were used. Changes in the cornea were examined histochemically using methods of choice for acid glycosidases, proteases, dehydrogenases, and Na(+)-K(+)-ATPase. SCL with high and low water content were worn in rabbits in 1, 2, 4, 7, 14, 21 and 28 days. Decreased activity of Na(+)-K(+)-ATPase, GGT, and SDH in the corneal endothelium and epithelium were not accompanied by detectable plasmin activity in the tear fluid. Pronounced damage of the corneal epithelium (increased activities of acid glycosidases, acid proteases, LDH, markedly decreased activity of SDH) was accompanied by low concentration of plasmin (0.4-1.0 micrograms/ml) in the tear fluid. Middle activity of plasmin (1.0-2.0 micrograms/ml) was detectable when PMNs were present in the corneal stroma. High plasmin activity (2.0-3.0 micrograms/ml) correlated with corneal ulceration and vascularization.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet-activating factor (PAF) accumulation correlates with injury in the cornea

This study reports the accumulation of platelet-activating factor (PAF) in corneas injured with either 0.1 N NaOH or 1 N NaOH. The degree of injury in corneas exposed to alkali for 5, 10, 20, or 60 sec was assessed by light microscopy and scanning electron microscopy. PAF accumulation in vivo increased with time (up to 24 hr) after injury and also according to the severity of the alkali injury. PAF was isolated by high-performance liquid chromatography (HPLC) and assayed by platelet aggregation of the HPLC fraction containing PAF. The specificity of the aggregating bioactivity was ascertained from inhibition of platelet aggregation by selective PAF antagonists. BN 50726, a new synthetic PAF antagonist, applied in vivo topically or subconjunctivally, was effective in inhibiting PAF formation. Because PAF is accumulated in vivo as soon as 30 min after corneal injury, this lipid mediator seems to be synthesized by corneal cells and not be recruited inflammatory cells, since they arrive later. Moreover, if the injury causes stromal edema and endothelial damage, the amount of PAF accumulated is even greater. Results from isolated corneas stimulated in vitro with calcium ionophore A23187 suggest that PAF synthesis is the result of stimulation of phospholipase A2 to form lyso-PAF and subsequent activation of an acetyltransferase.

Histochemical study of alkali-burned rabbit anterior eye segment in which severe lesions were prevented by aprotinin treatment

Activities of different enzymes (acid glycosidases, phosphatases, Na+ - K+ -dependent ATPase, proteases, dehydrogenases) and acid glycosaminoglycans were studied by histochemical methods in sections of rabbit anterior eye segments after experimental alkali burn and treatment with aprotinin, an inhibitor of plasmin and other serine proteinases. Solutions of sodium hydroxide (0.25-1.0 M) were applied on corneas using 12-mm-diameter plastic tube for 15-60 s. After wiping with cotton and rinsing with tap water aprotinin solutions were applied in saline (in experimental animals) and saline (in control animals) dropwise in 12-h intervals for a month. Within the first two weeks aprotinin was used at a concentration of 5000 IU/ml. During the subsequent two weeks the aprotinin concentration was reduced to 2500 IU/ml. Striking differences in enzyme activities and in the healing between treated and untreated eyes were found. Without aprotinin, ulcers developed in most corneas within 3 weeks and plasmin was regularly demonstrated in tears and in the aqueous. When aprotinin treatment was started within 24 h after the burn, the number of enzymatically active inflammatory cells was significantly lower, not only in the cornea itself but also in the whole anterior eye segment. With aprotinin treatment no ulcerations and no plasmin in tears and the aqueous were observed and the corneas healed within a month. The healing process started from the zone of enzymatically activated corneal cells in the unburned zone at the corneal periphery. In the regenerating epithelium and endothelium high activities of Na+ -K+ -dependent ATPase, gamma-glutamyltransferase, lactate and succinate dehydrogenases appeared very soon.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased cytochrome oxidase activity in alkali-burned corneas

Cytochrome oxidase (CO) activity on alkali-burned rabbit corneas was investigated histochemically to determine the metabolic change in inflamed corneas during wound healing. Cryostat sections of chemically burned and mechanically scraped corneas were stained for CO activity, which is regarded as an index of metabolic activity. Following chemical injury, positive CO activity was detected initially in the vascular endothelial cells of limbal blood vessels. Numerous active polymorphonuclear leukocytes (PMNs) and monocytes were found intravascularly and perivascularly. Fibroblasts that appeared at the wound site exhibited marked CO activity around the limbus. Over a period of 13 days, PMNs gradually invaded the central cornea, followed by fibroblasts of high metabolic activity. The areas of PMN infiltration were the same areas in which fibroblasts showed intense staining, suggesting that a PMN-derived mediator or secondary products might affect the activation of fibroblasts. Epithelial resurfacing was delayed in the chemically burned corneas, although reepithelialization was completed within two to three days in the scraped corneas. Limbal epithelial cells, which recently were suggested as the source of epithelial renewal, showed a remarkable increase of metabolic activity in response to chemical inflammatory stimulation, whereas those in the scraped model did not. This suggests that epithelial cell renewal at the limbus was accelerated in the presence of disturbed reepithelialization.

Epidermal growth factor in alkali-burned corneal epithelial wound healing

We conducted a double-masked study to evaluate the effect of epidermal growth factor on epithelial wound healing and recurrent erosions in alkali-burned rabbit corneas. Epithelial wounds 10 mm in diameter healed completely under the influence of topical epidermal growth factor, whereas the control corneas did not resurface in the center. On reversal of treatment, the previously nonhealing epithelial defects healed when treated with topical epidermal growth factor eyedrops. Conversely, the epidermal growth factor-treated and resurfaced corneas developed epithelial defects when treatment was discontinued. Histopathologic examination disclosed hyperplastic epithelium growing over the damaged stroma laden with polymorphonuclear leukocytes when treated with epidermal growth factor eyedrops, but it did not adhere to the underlying tissue. Hydropic changes were seen intracellularly as well as between the epithelial cells and the stroma.

Isoelectric focusing of sparingly soluble proteins in immobilized pH gradients, exemplified by microvillar membrane hydrolases

A novel fractionation technique is described for analysis of membrane-bound enzymes and sparingly soluble proteins: isoelectric focusing in a mixed-type matrix, containing a primary, immobilized pH gradient with a superimposed, secondary carrier ampholyte pH gradient. Three microvilli hydrolases: dipeptidyl peptidase IV, gamma-glutamyl transferase and alkaline phosphatase exhibit an array of sharply focused, enzyme active bands in the pH 4-6.5 range. The separation pattern obtained is by far superior to any separation achieved by either technique separately.