Brendan J. Quirk

Photodynamic therapy (PDT) for malignant brain tumors — Where do we stand?

INTRODUCTION What is the current status of photodynamic therapy (PDT) with regard to treating malignant brain tumors? Despite several decades of effort, PDT has yet to achieve standard of care. PURPOSE The questions we wish to answer are: where are we clinically with PDT, why is it not standard of care, and what is being done in clinical trials to get us there. METHOD Rather than a meta-analysis or comprehensive review, our review focuses on who the major research groups are, what their approaches to the problem are, and how their results compare to standard of care. Secondary questions include what the effective depth of light penetration is, and how deep can we expect to kill tumor cells. CURRENT RESULTS A measurable degree of necrosis is seen to a depth of about 5mm. Cavitary PDT with hematoporphyrin derivative (HpD) results are encouraging, but need an adequate Phase III trial. Talaporfin with cavitary light application appears promising, although only a small case series has been reported. Foscan for fluorescence guided resection (FGR) plus intraoperative cavitary PDT results were improved over controls, but are poor compared to other groups. 5-Aminolevulinic acid-FGR plus postop cavitary HpD PDT show improvement over controls, but the comparison to standard of care is still poor. CONCLUSION Continued research in PDT will determine whether the advances shown will mitigate morbidity and mortality, but certainly the potential for this modality to revolutionize the treatment of brain tumors remains. The various uses for PDT in clinical practice should be pursued.

Near-Infrared Photobiomodulation in an Animal Model of Traumatic Brain Injury: Improvements at the Behavioral and Biochemical Levels

OBJECTIVE The purpose of this was to evaluate the neuroprotective effects of near-infrared (NIR) light using an in-vivo rodent model of traumatic brain injury (TBI), controlled cortical impact (CCI), and to characterize changes at the behavioral and biochemical levels. BACKGROUND DATA NIR upregulates mitochondrial function, and decreases oxidative stress. Mitochondrial oxidative stress and apoptosis are important in TBI. NIR enhanced cell viability and mitochondrial function in previous in-vitro TBI models, supporting potential NIR in-vivo benefits. METHODS Sprague-Dawley rats were divided into three groups: severe TBI, sham surgery, and anesthetization only (behavioral response only). Cohorts in each group were administered either no NIR or NIR. They received two 670 nm LED treatments (5 min, 50 mW/cm(2), 15 J/cm(2)) per day for 72 h (chemical analysis) or 10 days (behavioral). During the recovery period, animals were tested for locomotor and behavioral activities using a TruScan device. Frozen brain tissue was obtained at 72 h and evaluated for apoptotic markers and reduced glutathione (GSH) levels. RESULTS Significant differences were seen in the TBI plus and minus NIR (TBI+/-) and sham plus and minus NIR (S+/-) comparisons for some of the TruScan nose poke parameters. A statistically significant decrease was found in the Bax pro-apoptotic marker attributable to NIR exposure, along with lesser increases in Bcl-2 anti-apoptotic marker and GSH levels. CONCLUSIONS These results show statistically significant, preclinical outcomes that support the use of NIR treatment after TBI in effecting changes at the behavioral, cellular, and chemical levels.

Therapeutic effect of near infrared (NIR) light on Parkinson's disease models.

Parkinsons disease (PD) is a neurodegenerative disorder that affects large numbers of people, particularly those of a more advanced age. Mitochondrial dysfunction plays a central role in PD, especially in the electron transport chain. This mitochondrial role allows the use of inhibitors of complex I and IV in PD models, and enhancers of complex IV activity, such as NIR light, to be used as possible therapy. PD models fall into two main categories; cell cultures and animal models. In cell cultures, primary neurons, mutant neuroblastoma cells, and cell cybrids have been studied in conjunction with NIR light. Primary neurons show protection or recovery of function and morphology by NIR light after toxic insult. Neuroblastoma cells, with a gene for mutant alpha-synuclein, show similar results. Cell cybrids, containing mtDNA from PD patients, show restoration of mitochondrial transport and complex I and IV assembly. Animal models include toxin-insulted mice, and alpha-synuclein transgenic mice. Functional recovery of the animals, chemical and histological evidence, and delayed disease progression show the potential of NIR light in treating Parkinsons disease.

Near-Infrared Irradiation Photobiomodulation: The Need for Basic Science

Near-infrared irradiation photobiomodulation (NIR-PBM) has been studied, discussed, and debated now for several decades. PBM is based on the theory that low level light in the NIR range can alter, and improve, cellular function.1 In particular, it is believed that NIR-PBM functions by improving mitochondrial energy production by stimulating the complex IV enzyme, cytochrome c oxidase (CCO), and increasing adenosine-5′-triphosphate (ATP) synthesis.2,3 Cellular effects attributed to NIR-PBM include increased ATP, reduced production of reactive oxygen species, protection against toxins, increased cellular proliferation, and reduction of apoptosis.2,3 Clinical uses of NIR-PBM have been studied in such diverse areas as wound healing,4,5 oral mucositis,6 and retinal toxicity.7 In addition, NIR-PBM is being considered for study in connection with areas such as aging and neural degenerative diseases (Parkinsons disease in particular).8 One thing that is missing in all of these pre-clinical and clinical studies is a proper investigation into the basic science of the NIR-PBM phenomenon. Although there is much discussion of the uses of NIR, there is very little on how it actually works. As far as explaining what really happens, we are basically left to resort to saying “light enters, then a miracle happens, and good things come out!” Clearly, this is insufficient, if for no other reason than our own intellectual curiosity. But beyond that, we can not hope to truly develop this extremely promising treatment to its highest potential without some understanding of what is actually happening inside the “black box”. Therefore, we maintain that the time has come to devote serious effort to the study of the basic science of NIR-PBM. At the heart of the matter is the question of enzyme kinetics. As it is generally agreed that the cellular target for the NIR is the enzyme CCO,2,3 an understanding of how the light affects its kinetic properties is the most logical place to start. At this point, there appears to be only one study directly addressing this question.9 An increase in the observed kinetic constant for the reaction of CCO with cytochrome c was observed at high enzyme/substrate ratios when the enzyme was irradiated with 630-nm laser light. In contrast, a lowering of the kinetic constant occurred at low enzyme/substrate ratios. A mechanistic interpretation of these results was not offered. Errede et al.10 have published a detailed study of CCO kinetics, with an analysis of the results in light of several proposed mechanisms. The deduced rate equation for the reaction is complex, and includes many parameters relating to various steps in the proposed mechanism. Pastores work could be expanded to include a study similar to Erredes, but with the inclusion of NIR. A study of the kinetics along these lines could reveal specifics of the effects of NIR, and lead to mechanistic insights. In particular, it could be possible, eventually, to relate the phenomenon of NIR-PBM to specific steps in the catalytic cycle. This type of work could also be extended to studies considering other parameters of NIR-PBM application. Most work to date has been using a hodgepodge of wavelengths, intensities, and durations. Wavelengths considered, and promoted, tend to vary from 630 to 880 nm, intensities vary from 10 to 50 mW/cm2, and fluences vary from 1 to 10 J/cm2. It appears that the parameters chosen are, in many cases, related more to convenience and practicality than to anything else. Although some investigators have introduced some variability into their experiments,11 controlled experimental design studies have yet to be performed. As information regarding the basic mechanisms of the NIR-PBM effect becomes developed, the situation becomes such that a statistical experimental design aimed at optimization would be profitable. As the haphazard choices of NIR parameters may miss, or understate, the benefits to be gained from PBM, a proper designed experiment may lead to a better understanding of how to best use NIR-PBM. Variables such as power and fluence can be studied using factorial designs, while wavelengths can be varied or combined by incorporating mixture design elements into the factorial studies. Not only basic kinetic parameters can be explored this way, but also factors affecting various other downstream in vitro and in vivo pre-clinical and clinical studies. In this manner, a strong knowledge base can be built up, driving efforts leading to eventual optimal clinical development. Other factors affecting the basic enzyme kinetics, and therefore the understanding of the mechanism, can also be addressed. In particular, the effect of enzyme inhibitors can be studied in relation to NIR exposure. A great deal of work has been done regarding the effects of NO,12,13 CO,14 CN-,11 and other inhibitors on the kinetics of CCO. In particular, a role for NO in NIR-PBM has been proposed.15 A thorough study of the effects of NIR application on the nature of these inhibitions could lead to a better understanding of the mechanistic basis for NIR-PBM. Further aspects of kinetics that might lead to insights into PBM might include the interactions, if any, of NIR-PBM kinetics with changes in temperature, pH, exposure times, and application sequencing, among others. The information gained in this regard might relate not only to mechanistic understandings, but could also affect eventual clinical uses of PBM. Of course, conclusions regarding mechanisms based on kinetics are somewhat speculative, without direct supporting evidence. CCO has been extensively studied spectroscopically, especially using ultraviolet-visible spectroscopy (UV-VIS)16,17and electron paramagnetic resonance (EPR)18 techniques, but there has been very little studied regarding changes caused by exposure to light.19 As kinetic studies generate new hypotheses regarding mechanisms, new experiments involving spectroscopy, particularly EPR, can be designed to further test these ideas. All of these studies, of course, presuppose a steady supply of pure, active, cytochrome c oxidase. Fortunately, there is no dearth of useful enzyme preparation procedures published.20–23 Although involving some initial work and expense, any extensive projects along these lines would benefit from a stable, reliable, in-house source of CCO in quantity. In sum, we feel that the time is right to move aside from limiting ourselves to studying only the downstream results of NIR-PBM, and aggressively pursue avenues leading to a basic understanding of the underlying science. We have seen basic science projects focusing on enzymes with no proven physiological role criticized as being a “solution in need of a problem.” In contrast, here we have a situation that clearly needs an understanding of the basic science, a “problem in need of a solution.”

Cardioprotection from Ischemia-Reperfusion Injury by Near-Infrared Light in Rats

UNLABELLED Abstract Objective: Myocardial reperfusion injury can induce further cardiomyocyte death and contribute to adverse cardiovascular outcomes after myocardial ischemia, cardiac surgery, or circulatory arrest. Exposure to near-infrared (NIR) light at the time of reoxygenation protects neonatal rat cardiomyocytes and HL-1 cells from injury. We hypothesized that application of NIR at 670 nm would protect the heart against ischemia-reperfusion injury. METHODS We assessed the protective role of NIR in in vivo and in vitro rat models of ischemia-reperfusion injury. RESULTS NIR application had no effect on the function of the nonischemic isolated heart, and had no effect on infarct size when applied during global ischemia. In the in vivo model, NIR commencing immediately before reperfusion decreased infarct size by 40%, 33%, 38%, and 77%, respectively, after regional ischemic periods of 30, 20, 15, and 10 min. Serum cardiac troponin I (cTnI) was significantly reduced in the 15 min group, whereas creatine kinase (CK) and lactate dehydrogenase (LDH) levels were not affected. CONCLUSIONS We have demonstrated the safety of NIR application in an in vitro rat isolated model. In addition, we have demonstrated safety and efficacy when using NIR for cardioprotection in an in vivo rat ischemia model, and that this cardioprotection is dependent upon some factor present in blood, but not in perfusion buffer. RESULTS show potential for cTnI, but not CK or LDH, as a biomarker for cardioprotection by NIR. NIR may have therapeutic utility in providing myocardial protection from ischemia-reperfusion injury.

Presumed hydrogen sulfide-mediated neurotoxicity after streptococcus anginosus group meningitis.

Hydrogen sulfide is an environmental toxicant and gaseous neurotransmitter. It is produced enterically by sulfur-reducing bacteria and invasive pathogens including Streptococcus anginosus group, Salmonella and Citrobacter. We describe putative focal hydrogen sulfide neurotoxicity after Streptococcus constellatus meningitis, treated with adjunctive sodium nitrite and hyperbaric oxygen therapy.