Effect of thermal preconditioning before excimer laser photoablation

Analysis of the outcomes of three different cross-linking protocols for treatment of paediatric keratoconus: A multicentre randomized controlled trial

PURPOSE

To analyse long-term outcomes of standard cross-linking (SCXL), accelerated cross-linking (ACXL) and transepithelial cross-linking (TCXL) in the treatment of progressive paediatric keratoconus regarding stability, safety and efficacy.

METHODS

This prospective multicentre randomized controlled trial included 97 eyes of 97 paediatric patients with stages I-III ABCD keratoconus grading system, who were randomized into three groups; SCXL group (control group, n = 32; 3 mW/cm2  × 30 min/5.4 J/cm2 ), ACXL (n = 33; 18 mW/cm2  × 5 min/5.4 J/cm2 ) and TCXL (n = 32; 18 mW/cm2  × 5 min/5.4 J/cm2 ). Subjective refraction, uncorrected and corrected visual acuity, keratometry and pachymetry measurements using corneal topography were recorded preoperatively and 1, 2 and 3 years postoperatively.

RESULTS

SCXL group exhibited significant successive improvements in the mean visual, refractive and keratometric parameters throughout the entire postoperative 3 years while ACXL group exhibited significant improvements in visual and keratometric parameters in the first postoperative year that remained stable in second and third postoperative years. TCXL group exhibited significant progressive deterioration in all mean parameters compared to SCXL and ACXL (p < 0.0001). Both SCXL and ACXL revealed final 100% success rate with good stability while TCXL revealed final 22% failure rate with keratoconus progression (p < 0.0001).

CONCLUSION

SCXL and ACXL were comparable in halting keratoconus progression and achieved good stability and safety; however, SCXL was more efficient than ACXL as it yielded greater significant postoperative mean visual, refractive and keratometric improvements achieving smoother corneal remodelling. Both SCXL and ACXL were much superior to TCXL. SCXL is the best CXL treatment option for paediatric keratoconus while ACXL is a good and effective alternative.

Evaluation of histologic, antiapoptotic and antioxidant effects of melatonin against the acute ocular toxicity of Cisplatin

This study aimed to investigate the protective effect of melatonin against the acute toxicity of cisplatin in ocular tissues. The eyes of 40 rats were divided into 4 groups: Control group (10 rats), Melatonin (Mel) group (10 rats), Cisplatin (Cis) group (10 rats), Melatonin (Mel) + Cisplatin (Cis) group (10 rats). Retina, cornea, and ciliary body tissues were examined after hematoxylin-eosin staining of sections obtained from the eyes and were scored for disorganization and degeneration. Apoptotic cells were counted for the retina, cornea, and ciliary body with the TUNEL (Terminal deoxynucleotidyl transferase dUTP nick end labeling) method. The total antioxidant status (TAS) / total oxidant status (TOS) of homogenized eye tissues were measured. While apoptotic cells were found to increase in the cornea of the Cisplatin (Cis) group, no difference was found regarding the retina and ciliary body cell count. An increased number of apoptotic cells in the cornea of the Cis group was found while there was a decrease in the group where Cisplatin and Melatonin were administered together (Mel+Cis group). There was no statistically significant difference amongst groups for TOS or TAS. Melatonin had a partial protective effect against histological damage.

Mitomycin C application after photorefractive keratectomy in high, moderate, or low myopia: Systematic review and meta-analysis

Photorefractive keratectomy (PRK) is considered a safe approach laser procedure with a clinical significance in correcting myopia results. PRK requires removing the whole superficial epithelium. The integrity of the epithelial basement membrane and the deposition of abnormal extracellular matrix can put the cornea in a probable situation for corneal haze formation. Mitomycin C (MMC) is applied after excimer laser ablation as a primary modulator for wound healing, limiting corneal haze formation. We aim to summarize the outcomes of MMC application after laser ablation. We searched Scopus, PubMed, Cochrane CENTRAL, and Web of Science till December 2020 using relevant keywords. The data were extracted and pooled as mean difference (MD) or risk ratio (RR) with a 95% confidence interval (CI), using Review Manager software (version 5.4). Our analysis demonstrated a statistically significant result for MMC application over the control group in terms of corneal haze formation postoperatively (RR = 0.29, 95% CI: [0.19, 0.45], P < 0.00001). Regarding corrected distance visual acuity (CDVA), no significant difference was observed between the MMC group and the control group (MD = 0.02; 95% CI: [-0.04, 0.07]; P = 0.56). Regarding the uncorrected distance visual acuity (UDVA), the analysis favored the MMC application with (MD -0.03, 95% CI: [-0.06, -0.00]; P = 0.05). There was no statistically significant increase in complications with MMC. In conclusion, MMC application after PRK is associated with a lower incidence of corneal haze formation with no statistically significant side effects. The long term effect can show improvement regarding UDVA favoring MMC. However, there is no significant effect of MMCs application regarding CDVA, and SE.

Thermal Injury Induces Small Heat Shock Protein in the Optic Nerve Head In vivo

Purpose

To investigate the induction pattern of various heat shock protein (HSP) in the optic nerve head after thermal stress using transpupillary thermotherapy (TTT) and to determine the dose-response relationship of thermal stress on the induction of various HSP.

Methods

The 810 nm diode laser with 50 um spot size was aimed to the center of optic nerve head of right eye of Norway brown rats. First, the various exposure powers (100, 120, 140mW) were used with the same exposure duration, 60 seconds, to investigate power dosing effect. Second, the various exposure durations (1, 2, 3, and 5 minutes) were applied under constant 100mW laser power to investigate time dosing effect. Left eyes were served as controls. To quantify HSP expression, enucleation was performed at 24 hours after TTT. HSP 27 and αB-crystallin inductions in optic nerve head were examined with Western blot.

Results

All type of HSP was observed in normal state. After thermal injury, the expression of HSP 27 were increased, and the αB-crystallin were decreased.

Conclusions

Induction pattern of each HSP in the optic nerve head were different after thermal injury. Some HSPs were induced or exhausted. Further research is needed on the characteristic functions and induction conditions of each HSP.

Three-year outcomes of mixed astigmatism correction with single-step transepithelial photorefractive keratectomy with a large ablation zone

PURPOSE

To evaluate refractive and visual outcomes of single-step transepithelial photorefractive keratectomy (transPRK) in the treatment of mixed astigmatism with the use of an aberration-neutral profile and large ablation zone.

SETTING

Nicolaus Copernicus University and Oftalmika Eye Hospital, Bydgoszcz, Poland.

DESIGN

Retrospective, observational case series.

METHODS

This study included patients who underwent transPRK to correct mixed astigmatism and completed the 3-year follow-up. Procedures were performed with an Amaris 750S excimer laser using an aberration-neutral profile and optical zone of 7.2 mm or more.

RESULTS

A total 48 eyes of 39 patients were included. Preoperatively, mean spherical manifest refraction was +1.37 ± 0.98 diopter (D) (0.25 to 4.00 D), and astigmatism was -4.00 ± 0.76 D (-2.25 to -6.00 D). Three years postsurgery, it was -0.17 ± 0.26 D and -0.41 ± 0.44 D, respectively. Attempted spherical equivalent correction within ±0.50 D was achieved in 45 eyes (94%) and cylindrical correction in 34 (71%). Preoperative corrected distance visual acuity (CDVA) was 20/20 or better in 38 eyes (79%), and postoperative uncorrected was 20/20 or better in 29 eyes (60.0%). No eye had lost 2 or more Snellen lines of CDVA, whereas 3 eyes (6%) gained 2 or more lines. In 4 eyes (8%), haze of low intensity was observed at the periphery, with scores between 0.5 and 1.0, and only 1 eye getting a score of 2 in 0- to 4-degree scale.

CONCLUSIONS

Mixed astigmatism correction with large-ablation-zone transPRK provided good results for efficacy, safety, predictability, and visual outcomes in a 3-year follow-up.

Thermal Load During Corneal Excimer Laser Ablation: Impact of Different Ablation Parameters

PURPOSE

To characterize the impact of different ablation parameters on the change in peak corneal temperature during corneal excimer laser ablation.

METHODS

Forty-two ablations were performed (21 on polymethylmethacrylate [PMMA] and 21 on porcine eyes) simulating photorefractive keratectomy (PRK), transepithelial PRK, and laser in situ keratomileusis (LASIK) treatments. Each ablation was recorded using infrared thermography. The change in peak corneal temperature was analyzed with respect to varying ablation parameters.

RESULTS

Excellent correlation between the temperature rise in PMMA and porcine eyes was found. The change in peak corneal temperature was significantly higher in myopic than in hyperopic corrections, ranging from 6 °C for hyperopic corrections to 16 °C for a -18.00 diopters (D) correction. The change decreased with larger optical zones. Of all analyzed metrics, the refractive correction together with the maximum slope of the treatment showed the best coefficient of determination. Transepithelial ablations led to a higher change in peak corneal temperature than pure stromal ablations. Isothermal lines as a function of the refractive correction and optical zone diameter were calculated with a hypersurface model. If keeping the change in peak corneal temperature below 8 °C is the limit, only 3.00 to 4.00 D can be treated (6.5 mm or larger optical zone); for 10 °C, a maximum of 7.00 D (7 mm or larger optical zone) can be treated and for 12 °C, 10.00 D can be treated (6 mm or larger optical zone).

CONCLUSIONS

The effect of different parameters on change in peak corneal temperature during corneal laser ablation could be quantitatively evaluated. Cooling the cornea may aid in avoiding thermal denaturation. This is particularly important for transepithelial ablations, which further increase the thermal load due to the extra ablation of the epithelium. [J Refract Surg. 2020;36(10):667-676.].

Khalil A, Tawfik M, Said A, Amer I, Nooreldin A, Said O, Reffat M, Anwar S, Badawi A. Standard cross-linking protocol versus accelerated and transepithelial cross-linking protocols for treatment of paediatric keratoconus: a 2-year comparative study

PURPOSE

To compare the efficacy, safety and stability of standard epithelium-off cross-linking (SCXL) versus accelerated epithelium-off cross-linking (ACXL) and transepithelial epithelium-on cross-linking (TCXL) in the treatment of progressive keratoconus (KC) in children.

METHODS

This prospective multicentre controlled trial included 271 eyes (136 children) with grade 1-3 progressive KC who were randomized to undergo SCXL (n = 91, as a control group), ACXL (n = 92) or TCXL (n = 88). Uncorrected and corrected distance visual acuity, subjective refraction, pachymetry, keratometry and corneal topography measurements were recorded preoperatively and 6, 12 and 24 months postoperatively.

RESULTS

At 1 year, there was no significant difference in uncorrected distance visual acuity, refractive sphere, cylinder, spherical equivalent or Kmax between the ACXL and SCXL groups; however, during year 2, ACXL regressed while SCXL continued to improve. After 2 years, there were significant differences in all visual, refractive and keratometric components between SCXL and both ACXL and TCXL (p < 0.0001) and between ACXL and TCXL (p < 0.0001). KC progressed in 5.4% of patients who had ACXL and 28.4% of those who had TCXL but in none of those who had SCXL. Vernal keratoconjunctivitis was documented in 43.3% of eyes that progressed postoperatively.

CONCLUSION

SCXL was more effective for paediatric KC and achieved greater stability than either ACXL or TCXL, and ACXL was superior to TCXL. SCXL also achieved marked improvement in both myopia and spherical equivalent; however, these refractive outcomes were unpredictable and uncontrollable. TCXL had a 28.4% failure rate within 2 years. SCXL is preferable for management of paediatric KC.

Standard cross-linking versus photorefractive keratectomy combined with accelerated cross-linking for keratoconus management: a comparative study

Purpose

To compare the safety and efficacy of standard 30 min epithelium‐off cross‐linking (CXL) versus photorefractive keratectomy (PRK) combined with accelerated epithelium‐off cross‐linking (AXL) for the treatment of progressive keratoconus (CXL‐Plus).

Methods

This study was a prospective multicentre comparative clinical study. A total of 125 eyes of 75 patients with grade 1 keratoconus and documented progression were divided into two groups. Group A included 58 eyes treated with standard CXL. Group B included 67 eyes treated with combined PRK and AXL. The recorded data included UDVA, CDVA, subjective and objective refraction, keratometry and pachymetry using corneal topographies preoperatively and postoperatively at 3, 6, 12 and 24 months of follow‐up.

Results

In group A, at 24 months of UDVA and CDVA were improved from 1.12 ± 0.38 and 0.58 ± 0.42 to 0.66 ± 0.20 and 0.20 ± 0.12 (LogMAR±SD). The spherical equivalent was reduced from 4.03 ± 1.18 to 1.78 ± 1.04 D. The cylinder reduction was 0.32 ± 0.19 D. In group B, at 24 months of UDVA and CDVA were improved from 1.26 ± 0.52 and 0.68 ± 0.36 to 0.58 ± 0.28 and 0.20 ± 0.16 (LogMAR ± SD). The spherical equivalent was reduced from 4.23 ± 0.95 to 1.92 ± 0.74 D. The cylinder reduction was ±1.76 D.

Conclusion

Surprisingly, standard CXL showed close results to CXL‐Plus at the 24th follow‐up month. Standard CXL acted as a stabilizing procedure associated with a late myopic component reduction. CXL‐Plus acted as a refractive and stabilizing procedure with an early effect on both the myopic and the astigmatic component but no later improvements. Standard CXL seems to be more powerful than AXL in its long‐term effect. Therefore, in the future, we want to test the combination of PRK with standard CXL.

High-speed recording of thermal load during laser trans-epithelial corneal refractive surgery using a 750Hz ablation system

PURPOSE

To evaluate the temperature rise of human cornea during trans-epithelial photorefractive keratectomy (trans-PRK) with a 750Hz excimer laser employing Intelligent Thermal Effect Control (ITEC) software.

METHODS

In this observational case series, trans-PRK ablation was performed on 5 eyes of 3 patients using an aspheric profile of a 750Hz excimer laser system. A high-resolution infrared camera with a frame-rate of 350 images per second was used to determine the corneal surface temperature. Images were taken sequentially, starting a few seconds prior to and ending a few seconds after the ablation. The maximum temperature of any pixel of a given image were recorded and graphed against time.

RESULTS

The baseline ocular surface temperature, immediately prior to the beginning of excimer laser, ranged from 32 to 34.9°C. The maximum ocular surface temperature until the epithelium was ablated ranged from 35.2 to 39.7°C. The maximum ocular surface temperature during stromal ablation with high and low fluence laser ranged from 32.9 to 36.5 and from 34.4 to 37.7°C respectively.

CONCLUSION

The ITEC software is effective in controlling the maximum temperature rise during laser ablation in the extremely challenging situation of trans-PRK involving high ablation volumes of almost 6000nl, potentially improving the outcomes. The ITEC system limited the maximum temperature to 39.7°C in the epithelium, and 37.7°C in the stroma. The epithelial temperature was always higher than stromal temperature (regardless of high or low fluence irradiation). Safety limit of 40°C found in the literature was never reached.

Shielding effect of the smoke plume by the ablation of excimer lasers

Background

Shielding and scattering effect of the smoke plume column ejected from the laser ablated material is a well-known phenomenon. Debris evacuation system of the excimer laser equipment removes these particles, but insufficient air flow can result in undesired refractive outcomes of the treatment. The aim of this study was to reveal the effect of the air flow speed on the actual ablation depth.

Methods

SCWIND AMARIS 500E flying spot excimer laser was tested in this study. A 150 μm phototherapeutic keratectomy (PTK) profile with 8 mm diameter was applied to the surface of polymethyl methacrylate (PMMA) plates. The velocity of the air flow was changed with adjustable air aspiration system. Ablation depth was measured with highly-precise contact micrometer.

Results

The prediction model was statistically significant, F(1,8) = 552.85, p < 0.001, and accounted for approximately 98.7% of variance of ablation (R² = 0.987, R²_adj = 0.986). Lower air flow speed resulted in a weaker ablation capability of the excimer laser.

Conclusion

Air flow generated by the aspiration equipment is a key factor for the predictable outcomes of refractive treatment. Therefore, manufacturer inbuilt debris removal system should be regularly checked and maintained to ensure proper clinical and predictable refractive results.

Corneal Breakthrough Haze After Photorefractive Keratectomy With Mitomycin C: Incidence and Risk Factors

PURPOSE

To identify preoperative and intraoperative factors affecting breakthrough corneal haze incidence after photorefractive keratectomy (PRK) with mitomycin C (MMC).

METHODS

In this retrospective study of PRK performed at the Care Vision Refractive Laser Center, Tel Aviv, Israel, a total of 7535 eyes (n = 3854 patients; mean age ± SD, 26 ± 6 years; 55% men) underwent PRK with intraoperative MMC application. Patients with histories of corneal pathology or surgery were excluded. Incidence, time of onset, and corneal haze severity were documented on follow-up of 118 ± 110 days. Eyes were grouped by preoperative refraction [low (≤-3D), moderate (-3D to -6D), or high (>-6D) myopia; low (≤3D) or high (>3D) astigmatism; low or high hyperopia]; by intraoperative time (above or below 40 seconds); and by MMC application time (above or below 40 seconds). The main outcome measures were incidence, onset time, and severity of corneal haze.

RESULTS

The haze incidence was 2.1% in eyes with high myopia versus 1.1% in those with low to moderate myopia (P = 0.002), and 3.5 times higher in eyes with high than with low astigmatism (P < 0.05). The overall incidence was higher in eyes treated for hyperopia (10.8%) than for myopia (1.3%) (P = 0.0001). In eyes with moderate myopia, the haze incidence was lower in MMC application time ≥40 seconds (0%) than in <40 seconds (1.3%) (P = 0.03). After surgery, a mild early haze incidence peaked at 68.8 ± 6 days and severe late haze at 115 ± 17 days (P = 0.02).

CONCLUSIONS

Hyperopic and large myopic or astigmatic corrections carry higher risk of haze. Longer MMC application might have beneficial haze prevention.

Heat-shock protein expression in canine corneal wound healing

OBJECTIVE

Heat-shock proteins, particularly the 70-kDa member (Hsp70), have been implicated in facilitating wound healing in multiple tissues. Expression and localization of three HSPs were assessed in normal and wounded canine corneas to elucidate a role in epithelial healing.

METHODS

Paraffin-embedded normal corneas, acute and repeatedly abraded corneas, and keratectomies of spontaneous chronic corneal epithelial defects (SCCEDs) were subjected to routine immunohistochemistry for Hsp27, 47, and 70 expression. Ex vivo corneal defects were created and treated with anti-HSPs or IgG controls, and wound healing was monitored. Primary cultures of canine corneal stromal fibroblasts and corneal epithelial cells were treated with exogenous Hsp70, and an artificial wound was created in vitro to monitor restoration of the monolayer.

RESULTS

Normal canine corneas exhibited constitutive expression of all HSPs evaluated. Inducible expression was demonstrated in acutely wounded tissues, and expression in the chronically abraded corneas was relocalized. All HSP expression was below the limits of detection in the epithelium of SCCED samples. Inhibition of HSPs in culture resulted in delayed wound healing when compared to controls. Hsp70-treated fibroblasts demonstrated significantly (P < 0.001) increased migration and proliferation compared to the vehicle control; however, there was no significant effect of exogenous Hsp70 on corneal epithelial cells.

CONCLUSIONS

These findings suggest that HSPs are induced in the normal canine cornea during re-epithelialization. Hsp70 expression is likely important for inducing the cytoarchitectural remodeling, migration, and proliferation necessary early in the canine corneal healing response, and suppressed expression may contribute to the pathophysiology of nonhealing defects.

Centration axis in refractive surgery

The human eye is an asymmetric optical system and the real cornea is not a rotationally symmetrical volume. Each optical element in the eye has its own optical and neural axes. Defining the optimum center for laser ablation is difficult with many available approaches. We explain the various centration approaches (based on these reference axes) in refractive surgery and review their clinical outcomes. The line-of-sight (LOS) (the line joining the entrance pupil center with the fixation point) is often the recommended reference axis for representing wavefront aberrations of the whole eye (derived from the definition of chief ray in geometrical optics); however pupil centration can be unstable and change with the pupil size. The corneal vertex (CV) represents a stable preferable morphologic reference which is the best approximate for alignment to the visual axis. However, the corneal light reflex can be considered as non-constant, but dependent on the direction of gaze of the eye with respect to the light source. A compromise between the pupil and CV centered ablations is seen in the form of an asymmetric offset where the manifest refraction is referenced to the CV while the higher order aberrations are referenced to the pupil center. There is a need for a flexible choice of centration in excimer laser systems to design customized and non-customized treatments optimally.

In vivo analysis of laser preconditioning in incisional wound healing of wild-type and HSP70 knockout mice with Raman spectroscopy

BACKGROUND AND OBJECTIVE

Laser preconditioning augments incisional wound healing by reducing scar tissue and increasing maximum tensile load of the healed wound [Wilmink et al. (2009) J Invest Dermatol 129(1): 205-216]. Recent studies have optimized treatments or confirmed results using HSP70 as a biomarker. Under the hypothesis that HSP70 plays a role in reported results and to better understand the downstream effects of laser preconditioning, this study utilized a probe-based Raman spectroscopy (RS) system to achieve an in vivo, spatio-temporal biochemical profile of murine skin incisional wounds as a function of laser preconditioning and the presence of HSP70.

STUDY DESIGN/MATERIALS AND METHODS

A total of 19 wild-type (WT) and HSP70 knockout (HSP70-/-) C57BL/6 mice underwent normal and laser preconditioned incisional wounds. Laser thermal preconditioning was conducted via previously established protocol (λ = 1.85 µm, H(0 ) = 7.64 mJ/cm(2) per pulse, spot diameter = 5 mm, Rep. rate = 50 Hz, τ(p) = 2 milliseconds, exposure time = 10 minutes) with an Aculight Renoir diode laser, with tissue temperature confirmed by real-time infrared camera measurements. Wound-healing progression was quantified by daily collection of a spatial distribution of Raman spectra. The results of RS findings were then qualified using standard histology and polarization microscopy.

RESULTS

Raman spectra yielded significant differences (t-test; α = 0.05) in several known biochemical peaks between WT and HSP70 (-/-) mice on wounds and in adjacent tissue early in the wound-healing process. Analysis of peak ratios implied (i) an increase in protein configuration in and surrounding the wound in WT mice, and (ii) an increased cellular trend in WT mice that was prolonged due to laser treatment. Polarization microscopy confirmed that laser treated WT mice showed increased heterogeneity in collagen orientation.

CONCLUSIONS

The data herein supports the theory that HSP70 is involved in normal skin protein configuration and the cellularity of early wound healing. Laser preconditioning extends cellular trends in the presence of HSP70. Despite study limitations, RS provided a non-invasive method for quantifying temporal trends in altered wound healing, narrowing candidates and design for future studies with clinically applicable instrumentation.

Pulse duration determines levels of Hsp70 induction in tissues following laser irradiation

Induction of heat shock protein (Hsp) expression correlates with cytoprotection, reduced tissue damage, and accelerated healing in animal models. Since Hsps are transcriptionally activated in response to stress, they can act as stress indicators in burn injury or surgical procedures that produce heat and thermal change. A fast in vivo readout for induction of Hsp transcription in tissues would allow for the study of these proteins as therapeutic effect mediators and reporters of thermal stress∕damage. We used a transgenic reporter mouse in which a luciferase expression is controlled by the regulatory region of the inducible 70 kilodalton (kDa) Hsp as a rapid readout of cellular responses to laser-mediated thermal stress∕injury in mouse skin. We assessed the pulse duration dependence of the Hsp70 expression after irradiation with a CO(2) laser at 10.6 μm in wavelength over a range of 1000 to 1 ms. Hsp70 induction varied with changes in laser pulse durations and radiant exposures, which defined the ranges at which thermal activation of Hsp70 can be used to protect cells from subsequent stress, and reveals the window of thermal stress that tissues can endure.

Role of HSP70 in cellular thermotolerance

BACKGROUND AND OBJECTIVE

Thermal pretreatment has been shown to condition tissue to a more severe secondary heat stress. In this research we examined the particular contribution of heat shock protein 70 (HSP70) in thermal preconditioning.

STUDY DESIGN/MATERIALS AND METHODS

For optimization of preshock exposures, a bioluminescent Hsp70-luciferase reporter system in NIH3T3 cells tracked the activation of the Hsp70 gene. Cells in 96-well plates were pretreated in a 43 degrees C water bath for 30 minutes, followed 4 hours later with a severe heat shock at 45 degrees C for 50 minutes. Bioluminescence was measured at 2, 4, 6, 8, and 10 hours after preshock only (PS) and at 4 hours after preshock with heatshock (PS+HS). Viability was assessed 48 hours later with a fluorescent viability dye. Preshock induced thermotolerance was then evaluated in hsp70-containing Murine Embryo Fibroblast (+/+) cells and Hsp70-deficient MEF cells (-/-) through an Arrhenius damage model across varying temperatures (44.5-46 degrees C).

RESULTS

A time gap of 4 hours between preconditioning and the thermal insult was shown to be the most effective for thermotolerance with statistical confidence of P<0.05. The benefit of preshocking was largely abrogated in Hsp70-deficient cells. The Arrhenius data showed that preshocking leads to increases in the activation energies, E(a), and increases in frequency factors, A. The frequency factor increase was significantly greater in Hsp70-deficient cells.

CONCLUSION

The data shows that HSP70 contributes significantly to cellular thermotolerance but there are other pathways that provide residual thermotolerance in cells deficient in Hsp70.

Low Power Laser Irradiation Stimulates the Proliferation of Adult Human Retinal Pigment Epithelial Cells in Culture

We investigated the effects of low power laser irradiation on the proliferation of retinal pigment epithelial (RPE) cells. Adult human RPE cells were artificially pigmented by preincubation with sepia melanin, and exposed to a single sublethal laser pulse (590 nm, 1 µs, <200 mJ/cm²). DNA synthesis, cell number, and growth factor activity in irradiated RPE cells were subsequently monitored. The effect of sublethal laser irradiation on the "wound" healing response of an RPE monolayer in an in vitro scratch assay was also investigated. Single pulsed laser irradiation increased DNA synthesis in pigmented RPE cells measured 6 h post-treatment. In the scratch assay, laser irradiation increased the rates of cell proliferation and wound closure. Conditioned medium, collected 48 h following laser treatment, increased cell proliferation of unirradiated cells. Irradiation increased RPE cell secretion of platelet-derived growth factor (PDGF)-B chain, and increased mRNA levels of several growth factors and their receptors, including PDGF, transforming growth factor-β1, basic fibroblast growth factor, epidermal growth factor, insulin-like growth factor, as well as heat shock proteins. This demonstrates, for the first time, that low power single pulsed laser irradiation stimulates the proliferation of RPE cells, and upregulates growth factors that are mitogenic for RPE cells.

Molecular imaging-assisted optimization of hsp70 expression during laser-induced thermal preconditioning for wound repair enhancement

Patients at risk for impaired healing may benefit from prophylactic measures aimed at improving wound repair. Several photonic devices claim to enhance repair by thermal and photochemical mechanisms. We hypothesized that laser-induced thermal preconditioning would enhance surgical wound healing that was correlated with hsp70 expression. Using a pulsed diode laser (lambda=1.85 microm, tau(p)=2 ms, 50 Hz, H=7.64 mJ cm(-2)), the skin of transgenic mice that contain an hsp70 promoter-driven luciferase was preconditioned 12 hours before surgical incisions were made. Laser protocols were optimized in vitro and in vivo using temperature, blood flow, and hsp70-mediated bioluminescence measurements as benchmarks. Biomechanical properties and histological parameters of wound healing were evaluated for up to 14 days. Bioluminescent imaging studies indicated that an optimized laser protocol increased hsp70 expression by 10-fold. Under these conditions, laser-preconditioned incisions were two times stronger than control wounds. Our data suggest that this molecular imaging approach provides a quantitative method for optimization of tissue preconditioning and that mild laser-induced heat shock may be a useful therapeutic intervention prior to surgery.