Toxicologic pathology is a biomedical specialty that applies the tool kit for diagnostic pathology (the study of diseases) to toxicology (the study of poisons). The melding of toxicology with pathology is essential in assessing the safety of new materials.
Such materials often are classic poisons (termed “toxicants”) like industrial chemicals, metals, or small molecule drugs. In recent years, new types of materials have been developed, including biomolecules (nucleic acids and proteins), cell therapies, gene therapies, gene editing therapies, medical devices, and many more.
Toxicologic pathologists evaluate the ability of such materials to disrupt the structure of cells, tissues, and organs as well as change the composition of body fluids. The primary purpose of toxicologic pathology is to identify and characterize any hazards that might impact the health of humans, animals, or environment.
Dr. Bolon’s practice of toxicologic pathology encompasses both mainstream and fringe aspects of basic and applied biomedical research. His veterinary medical and advanced pathology training have fitted him to address a broad spectrum of biological questions. His primary interests and aptitudes in toxicologic pathology include:
This toxicologic pathology sub-specialty evaluates effects that develop in organs of the central nervous system (CNS = brain and spinal cord) and peripheral nervous system (PNS = ganglia and nerves) in developing (embryonic, fetal, and juvenile) or adult animals and people.
Dr. Bolon has published extensively in this area, coauthoring many well-recognized papers, book chapters, and a standard reference book on basic neurobiology, effective sampling and processing of neural organs, developmental neurotoxicity testing, neurotoxicity screening, and regulatory affairs. His major roles in this branch of toxicologic pathology are:
- to perform pathology peer reviews and occasional primary evaluations of microscopic changes in CNS and PNS tissues from animal toxicity studies designed to assess the safety of new therapeutic candidates for treating nervous system diseases, and
- to support basic research with new animal or in vitro models of CNS and PNS diseases.
Harmful effects produced by innovative therapies differ in many respects from the toxicity caused by classic toxicants like chemicals, metals, and small molecule drugs. In addition to direct toxicity associated with their intended molecular action, novel modalities may be associated with other undesirable effects such as gene disruption and immunogenicity.
Dr. Bolon has considerable experience in analyzing and interpreting changes associated with administration of several classes of unusual materials that have gained acceptance in recent years as treatments for unmet medical needs:
This modality consists of materials derived from biological materials. Common types include engineered (recombinant) proteins, synthesized peptides, and synthesized oligonucleotides. Toxicologic pathology examination of these materials assesses not only direct tissue toxicity but also the extent and severity of any immune response to the biomolecule.
This modality introduces new cells (often modified stem cells) to replace nonfunctional cells within a diseased organ. The cells may be engineered prior to their administration to optimize their survival and function. Toxicologic pathology assessments of engrafted cells will not only search for proper cell incorporation but also for the degree of trauma and repair at the site of cell insertion. Stem cells designed to have an extended lifespan also will be examined for unwelcome side effects like inappropriate differentiation and neoplastic transformation.
This modality inserts one or more engineered genes to restore the function of a missing protein or reduce the undesirable activity of an existing protein. Products that have been recently approved typically deliver the engineered gene using a viral vector, but other non-viral delivery systems also are being developed. Toxicologic pathology evaluation of these products must assess the safety of the engineered gene and the delivery system.
Gene Editing Therapy
This modality uses enzymes to deactivate, remove, or replace faulty genes. Products now under investigation are testing CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) technology as a means for editing genes outside or even inside the body. Toxicologic pathology screening for such products must investigate the safety of the CRISPR and Cas (CRISPR-associated) components as well as the delivery vehicle (often a viral vector).
Medical Devices (for nervous system use)
Devices are implanted to either correct a problem directly (such as a pacemaker) or to serve as a portal for delivering a therapeutic agent (such as a catheter). Toxicologic pathology evaluations of devices examine the reaction of tissues near the implantation site as well as the tendency to cause any trauma to the delicate nearby neural tissues.
Peer reviews serve as a quality control (QC) procedure for microscopic data sets from animal toxicity studies. The Peer Review Pathologist cross-checks the diagnoses and interpretations of the original Study Pathologist to maximize the quality of the data set. Dr. Bolon typically serves as a Peer Review Pathologist in two situations:
The discipline of toxicologic pathology offers a rich tableau of roles from which to choose. In addition to such routine tasks as neuropathology evaluations and pathology peer reviews, Dr. Bolon also contributes to the toxicologic pathology profession by:
- Bolon B (2000). Comparative and correlative neuroanatomy for the toxicologic pathologist. Toxicol Pathol 28(1): 6-27
- Bolon B, Bradley A, Garman RH, Krinke GJ (2011). Useful toxicologic neuropathology references for pathologists and toxicologists. Toxicol Pathol 39(1): 234-239
- Vernau W, Vernau KM, Bolon B (2011). Cerebrospinal fluid analysis in toxicological neuropathology. In: Fundamental Neuropathology for Pathologists and Toxicologists: Principles and Techniques (Bolon B, Butt MT, eds.). John Wiley & Sons, Hoboken, NJ, pp. 271-283
- Ramos M, Reilly CM, Bolon B (2011). Toxicologic pathology of the retina and optic nerve. In: Fundamental Neuropathology for Pathologists and Toxicologists: Principles and Techniques (Bolon B, Butt MT, eds.). John Wiley & Sons, Hoboken, NJ, pp. 385-412.
- Forge A, Taylor R, Bolon B (2011). Toxicologic pathology of the ear. In: Fundamental Neuropathology for Pathologists and Toxicologists: Principles and Techniques (Bolon B, Butt MT, eds.). John Wiley & Sons, Hoboken, NJ, pp. 413-428.
- Genter MB, Bolon B (2011). Toxicologic pathology of the olfactory system. In: Fundamental Neuropathology for Pathologists and Toxicologists: Principles and Techniques (Bolon B, Butt MT, eds.). John Wiley & Sons, Hoboken, NJ, pp. 429-448.
- Bolon B (2011). Ready references of neurobiology knowledge. In: Fundamental Neuropathology for Pathologists and Toxicologists: Principles and Techniques (Bolon B, Butt MT, eds.). John Wiley & Sons, Hoboken, NJ, pp. 541-562.
- Hagan C, Bolon B, Keene CD (2011). Nervous system. In: Comparative Anatomy and Histology: A Mouse and Human Atlas (Treuting PM, Dintzis S, eds.). Academic Press (Elsevier), San Diego, pp. 339-394
- Bolon B, Butt MT, Garman RH, Dorman DC (2013). Nervous system. In: Haschek and Rousseaux’s Handbook of Toxicologic Pathology, 3rd ed. (Haschek WM, Rousseaux CG, Wallig MA, Bolon B, Ochoa R, Mahler BW, eds.). Academic Press (Elsevier), San Diego, pp. 2005-2093.
- Schafer KA, Bolon B (2013). Ear. In: Haschek and Rousseaux’s Handbook of Toxicologic Pathology, 3rd ed. (Haschek WM, Rousseaux CG, Wallig MA, Bolon B, Ochoa R, Mahler BW, eds.). Academic Press (Elsevier), San Diego, pp. 2187–2218.
- Chen VS, Morrison JM, Southwell M, Foley JF, Bolon B, Elmore SA (2017). Histology atlas of the developing prenatal and postnatal mouse central nervous system, with emphasis on prenatal days E7.5 to E18.5. Toxicol Pathol 45(6): 705-744. [Featured article on cover].
- Snyder JM, Hagan CE, Bolon B, Keene CD (2017). Nervous system. In: Comparative Anatomy and Histology: A Mouse, Rat, and Human Atlas, 2nd ed. (Treuting PM, Dintzis S, Montine KS, eds.). Academic Press (Elsevier), San Diego, pp. 403-444
- Bolon B, Krinke GJ, Pardo ID (2020). Essential references for structural analysis of the peripheral nervous system (PNS) for toxicologic pathologists and toxicologists. Toxicol Pathol 48(1): 87-95
- Pardo ID, Weber K, Krinke GJ, Cramer S, Butt MT, Sharma AK, Bolon B (2020). Atlas of normal micronatomy, processing artifacts, common background findings, and key neurotoxic lesions in ganglia and nerves of the vertebrate peripheral nervous system. Toxicol Pathol 48(1): 105-131
- Bolon B (2017). Regulatory Forum opinion piece: Effective sectioning of spinal cord during regulatory-type nonclinical toxicity studies. Toxicol Pathol 45(5): 580-583
- Bolon B (2018). Regulatory Forum opinion piece: Effective brain trimming for regulatory-type nonclinical toxicity studies. Toxicol Pathol 46(2): 115-120
- Bolon B, Krinke G, Butt MT, Rao DB, Pardo ID, Jortner BS, Garman RH, Jensen K, Andrews-Jones L, Morrison JP, Sharma AK, Thibodeau MK (2018). STP position paper: Recommended best practices for sampling, processing and analysis of the peripheral nervous system (nerves and somatic and autonomic ganglia) during nonclinical toxicity studies. Toxicol Pathol 46(4): 372-402. [STP position paper on recommended (“best”) practices]
- Bolon B, Garman RH, Pardo ID, Jensen K, Sills RC, Roulois A, Radovsky AE, Bradley A, Andrews-Jones L, Butt M, Gumprecht L (2013). STP position paper: Recommended practices for sampling and processing the nervous system (brain, spinal cord, nerve, and eye) during nonclinical general toxicity studies. Toxicol Pathol 41(7): 1028-1048. [STP position paper on recommended (“best”) practices]
- Valentine W, Bolon B (2011). Anatomy and processing of peripheral nerve tissues. In: Fundamental Neuropathology for Pathologists and Toxicologists: Principles and Techniques (Bolon B, Butt MT, eds.). John Wiley & Sons, Hoboken, NJ, 229-237
- Bolon B, Butt MT (2014) Fixation and processing of central nervous system tissue. In: Encyclopedia of Neurological Sciences, 2nd ed., vol. 2 (Aminoff MJ, and Daroff RB, eds), Academic Press (Elsevier), San Diego, 2014, pp. 312-316
- Fortin JS, Chlipala EA, Shaw DP, Bolon B (2020). Methods optimization for routine sciatic nerve processing in animal toxicity studies. Toxicol Pathol 48(1): 19-29
Development Neurotoxicity Testing
- Bolon B, Garman R, Jensen K, Krinke G, Stuart B (2006). A ‘best practices’ approach to neuropathologic assessment in developmental neurotoxicity testing – for today. Toxicol Pathol 34(3): 296-313. [STP position paper on recommended (“best”) practices]
- Bolon B, Garman RH, Gundersen HJG, Johnson GA, Kaufmann W, Krinke G, Little PB, Makris SL, Mellon RD, Sulik KK, Jensen K (2011). Continuing education course #3: Current practices and future trends in neuropathology assessment for developmental neurotoxicity testing. Toxicol Pathol 39(1): 289-293
- Garman RH, Li AA, Kaufmann W, Auer RN, Bolon B (2016). Recommended methods for brain processing and quantitative analysis in rodent developmental neurotoxicity studies. Toxicol Pathol 44(1): 14-42. [Featured article on cover, and 2017 “best original research paper” award for journal.]
- Li AA, Sheets LP, Raffaele K, Moser V, Hofstra A, Hoberman A, Makris SL, Garman R, Bolon B, Kaufmann W, Auer R, Lau E, Vidmar T, Bowers WJ (2017). Recommendations for harmonization of data collection and analysis of developmental neurotoxicity endpoints in regulatory guideline studies: Proceedings of workshops presented at the Society of Toxicology and joint Teratology Society and Neurobehavioral Teratology Society meetings. Neurotoxicol Teratol 63: 24-45
- Li AA, Garman RH, Sheets LP, Bowers WJ, Kaufmann W, Auer RN, Bolon B (2018). Regulatory testing for developmental neurotoxicology. In Comprehensive Toxicology, 3rd ed, Vol. 9 (McQueen CA, ed.). Elsevier Ltd., Oxford, pp. 183–215
- Bolon B, Anthony DC, Butt M, Dorman D, Green MV, Little P, Valentine WM, Weinstock D, Yan J, Sills R (2008). Current pathology techniques symposium review: Advances and issues in neuropathology. Toxicol Pathol 36(6): 871-889
- Morrison JP, Sharma AK, Rao D, Pardo ID, Garman RH, Kaufmann W, Bolon B (2015). Fundamentals of translational neuroscience in toxicologic pathology: optimizing the value of animal data for human risk assessment. Toxicol Pathol 43(1): 132-139
- Teased nerve fibers
- Bolon B, Pardo ID, Krinke GJ (2020). The science and art of nerve fiber teasing for myelinated nerves: Methodology and interpretation. Toxicol Pathol 48(1): 49-58
- Bolon B, Bradley A, Butt M, Jensen K, Krinke G, Mellon RD (2011). Compilation of international regulatory guidance documents for neuropathology assessment during nonclinical toxicity studies. Toxicol Pathol 39(1): 92-96
- Bolon B, Baze W, Shilling CJ, Keatley KL, Patrick DJ, Schafer KA (2018). Good laboratory practice (GLP) in the academic setting: Fundamental principles for nonclinical safety assessment and GLP-compliant pathology support when developing innovative biomedical products. ILAR J 59(1):18-28
- Bolon B, Bradley A, Butt MT, Jensen K, Rao DB (2020). International regulatory guiding documents and best practice recommendations on peripheral nervous system (PNS) histopathologic evaluation in Good Laboratory Practice (GLP)-compliant animal toxicity studies. Toxicol Pathol 48(1): 78-86
Reference Book on Toxicologic Neuropathology
- Bolon B and Butt MT (2011). Fundamental Neuropathology for Pathologists and Toxicologists: Principles and Techniques. John Wiley & Sons, Hoboken, NJ, 590 pp
Pathology of Novel Modalities
- Campagnuolo G,1 Bolon B,1 Feige U (2002). Kinetics of bone protection by recombinant osteoprotegerin (OPG) therapy in Lewis rats with adjuvant arthritis. Arthritis Rheum 46(7): 1926-1936. [1Equal contributors]
- Bolon B, Jing S, Asuncion F, Scully S, Pisegna M, Van G, Hu Z, Yu YB, Min H, Wild K, Rosenfeld RD, Tarpley J, Carnahan J, Duryea D, Hill D, Kaufman S, Yan X-Q, Juan T, Christensen K, McCabe J, Simonet WS (2004). The candidate neuroprotective agent artemin induces autonomic neural dysplasia without preventing peripheral nerve dysfunction. Vet Pathol 32(3): 275-294. [Inaugural “best paper” award for journal.]
- Irizarry Rovira AR, Bennet BM, Bolon B, Braendli-Baiocco A, Chandra S, Fleurance R, Garman R, Hutto D, Lane J, Romeike A, Sargeant A, Zimmerman B (2018). Scientific and Regulatory Policy Committee Points to Consider: Histopathologic evaluation in safety assessment studies for PEGylated pharmaceutical products. Toxicol Pathol 46(6): 616-635. [Featured article on cover]
- Puig-Saus C, Parisi G, Garcia-Diaz A, Krystofinski PE, Sandoval S, Zhang R, Champhekar AS, McCabe J, Cheung-Lau GC, Truong NA, Vega-Crespo A, Komenan MDS, Pang J, Macabali MH, Saco JD, Goodwin JL, Bolon B, Seet CS, Montel-Hagen A, Crooks GM, Hollis RP, Campo-Fernandez B, Bischof D, Cornetta K, Gschweng EH, Adelson C, Nguyen A, Yang L, Witte ON, Baltimore D, Comin-Anduix B, Kohn DB, Wang X, Cabrera P, Kaplan-Lefko PJ, Berent-Maoz B, Ribas A (2019). IND-enabling studies for a clinical trial to genetically program a persistent cancer-targeted immune system. Clin Cancer Res. 25(3): 1000-1011
- Bolon B, Carter C, Daris M, Morony S, Capparelli C, Hsieh A, Mao M, Kostenuik P, Dunstan CR, Lacey DL, Sheng J (2001). Adenoviral delivery of osteoprotegerin ameliorates bone resorption in a mouse ovariectomy model of osteoporosis. Mol Ther 3(2): 197-205
- Murrey DA, Naughton BJ, Duncan FJ, Meadows AS, Ware TA, Campbell KJ, Bremer WG, Walker CM, Goodchild L, Bolon B, La Perle K, Flanigan KM, McBride KL, McCarty DM, Fu H (2014). Feasibility and safety of systemic rAAV9-hNAGLU delivery for treating mucopolysaccharidosis IIIB: toxicology, bio-distribution and immunological assessments in primates. Hum Gene Ther Clin Dev 25(2): 72-84
- Meadows AS, Duncan FJ, Camboni M, Waligura K, Montgomery C, Zaraspe K, Naughton BJ, Bremer WG, Shilling C, Walker CM, Bolon B, Flanigan KM, McBride KL, McCarty DM, Fu H (2015). A GLP-compliant toxicology and biodistribution study: Systemic delivery of an rAAV9 vector for the treatment of mucopolysaccharidosis IIIB. Hum Gene Ther Clin Dev 26: 228-242
Pathology Peer Review
- McKay JS, Barale-Thomas E, Bolon B, George C, Hardisty J, Manabe S, Schorsch F, Teranishi M, Weber K. A commentary on the process of peer review and pathology data locking. Toxicol Pathol 38(3): 508-510, 2010
- Morton D, Sellers R, Barale-Thomas E, Bolon B, George C, Hardisty J, Irizarry A, McKay JS, Odin M, Teranishi M (2010). Recommendations for pathology peer review. Toxicol Pathol 38(7): 1118-1127 [STP position paper on recommended (“best”) practices]
Toxicologic Pathology Practice
Best Practices in Toxicologic Pathology
- Everds N, Snyder P, Bailey K, Bolon B, Creasy D, Foley G, Rosol T, Sellers T (2013). Interpreting stress responses during routine toxicology studies: a review of the biology, impact, and assessment. Toxicol Pathol 41(4): 560-614 [featured article on cover]
- Kerlin R, Bolon B, Burkhardt J, Francke S, Greaves P, Meador V, Popp J (2016). Recommended (“best”) practices for determining, communicating and using adverse effect data from nonclinical studies. Toxicol Pathol 44(2): 147-162. [STP position paper on recommended (“best”) practices]
- Aeffner F, Wilson K, Martin NT, Black JC, Luengo Hendriks CL, Bolon B, Rudmann DG, Gianani R, Koegler SR, Krueger J, Young GD (2017). The “gold standard” paradox in digital image analysis: Manual vs. automated scoring as ground truth. Arch Pathol Lab Med 141(9): 1267-1275
- Bolon B, Caverly Rae J, Colman K, Francke S, Jensen K, Keane K, McInnes EF, Nakano-Ito K, Perry R, Polack E, Regan KS, Romeike A, Young JK, Galbreath EJ (2020). Toxicologic Pathology Forum: Opinion on current use of non-blinded versus blinded histopathologic evaluation in animal toxicity studies. Toxicol Pathol 48(4):549-559
- Kaufmann W, Bolon B, Bradley A, Butt M, Czasch S, Garman RH, George C, Gröters S, Krinke G, Little P, McKay J, Narama I, Rao D, Shibutani M, Sills R (2012). Proliferative and non-proliferative lesions of the rat and mouse central and peripheral nervous systems. Toxicol Pathol 40(4 Suppl): 87S-157S
- Fossey S, Vahle J, Long P, Schelling S, Ernst H, Boyce RW, Jolette J, Bolon B, Bendele A, Rinke M, Healy L, High W, Roth DR, Boyle M, Leininger J (2016). Nonproliferative and proliferative lesions of the rat and mouse skeletal tissues (bones, joints, and teeth). J Toxicol Pathol 29 (3 Suppl): 49S-103S
Training of Toxicologic Pathologists
- Bolon B, Ochoa R, Mann P (2009). Commentary: STP debate on the desirability of an international mechanism for recognizing qualified toxicologic pathologists. Toxicol Pathol 37(7): 992-996
- Bolon B, Barale-Thomas E, Bradley A, Ettlin RA, Franchi CAS, George C, Giusti AM, Hall R, Jacobsen M, Konishi Y, Ledieu D, Morton D, Park J-H, Scudamore C, Tsuda H, Vijayasarathi SK, Wijnands MVW. International recommendations for training future toxicologic pathologists participating in regulatory-type, nonclinical toxicity studies. Toxicol Pathol 38(6): 984-992, 2010
- Turner PV, Haschek WM, Bolon B, Diegel K, Hayes MA, McEwen B, Sargeant AM, Scudamore CL, Stalker M, von Beust B, Wancket LM (2015). Commentary: The role of the toxicologic pathologist in academia. Vet Pathol 52(1): 7-17