Peripheral Neuropathy in Rat Models of Type 2 Diabetes (AQA 2022) PDF

Review Complications Diabetes Metab J 2022;46:198-221 https://doi.org/10.4093/dmj.2021.0347 pISSN 2233-6079 · eISSN 2233-6087 DIABETES & METABOLISM JOURNAL Peripheral Neuropathy Phenotyping in Rat Models of Type 2 Diabetes Mellitus: Evaluating Up...

Review Complications Diabetes Metab J 2022;46:198-221 https://doi.org/10.4093/dmj.2021.0347 pISSN 2233-6079 · eISSN 2233-6087 DIABETES & METABOLISM JOURNAL Peripheral Neuropathy Phenotyping in Rat Models of Type 2 Diabetes Mellitus: Evaluating Uptake of the Neurodiab Guidelines and Identifying Future Directions Md Jakir Hossain1, Michael D. Kendig1, Meg E. Letton2, Margaret J. Morris1, Ria Arnold1,2,3 Departments of 1Pharmacology, 2Exercise Physiology, School of Medical Sciences, University of New South Wales (UNSW) Sydney, Sydney, 3 Department of Exercise and Rehabilitation, School of Medical, Indigenous and Health Science, University of Wollongong, Wollongong, Australia Diabetic peripheral neuropathy (DPN) affects over half of type 2 diabetes mellitus (T2DM) patients, with an urgent need for ef- fective pharmacotherapies. While many rat and mouse models of T2DM exist, the phenotyping of DPN has been challenging with inconsistencies across laboratories. To better characterize DPN in rodents, a consensus guideline was published in 2014 to accelerate the translation of preclinical findings. Here we review DPN phenotyping in rat models of T2DM against the ‘Neurodi- ab’ criteria to identify uptake of the guidelines and discuss how DPN phenotypes differ between models and according to diabetes duration and sex. A search of PubMed, Scopus and Web of Science databases identified 125 studies, categorised as either diet and/ or chemically induced models or transgenic/spontaneous models of T2DM. The use of diet and chemically induced T2DM mod- els has exceeded that of transgenic models in recent years, and the introduction of the Neurodiab guidelines has not appreciably increased the number of studies assessing all key DPN endpoints. Combined high-fat diet and low dose streptozotocin rat models are the most frequently used and well characterised. Overall, we recommend adherence to Neurodiab guidelines for creating bet- ter animal models of DPN to accelerate translation and drug development. Keywords: Diabetes mellitus, type 2; Diabetic neuropathies; Diet, high-fat; Models, animal; Models, genetic; Peripheral nerves; Rats; Streptozotocin INTRODUCTION deciphered. A consequence of the rising global prevalence of diabetes and prediabetes is a corresponding increase in Diabetes is a global health concern that cuts across socioeco- DPN. DPN manifests as a distal symmetric polyneuropathy af- nomic status and national boundaries. In 2019, the Interna- fecting the lower extremities in a length-dependent fashion tional Diabetes Federation estimated that 463 million adults and is primarily a disorder of sensory dysfunction character- are living with diabetes and 374 million with impaired glucose ized by pain, allodynia, numbness, and insensate feet. These tolerance, predicted to rise to 700 million and 548 million, re- initial manifestations can progress to physical impairments spectively, by 2045. Diabetic peripheral neuropathy (DPN) (e.g., loss of balance) and an increased risk of falls, foot ulcer- is the most prevalent complication in diabetes, affecting more ation, amputation and mortality [4,5]. Despite dramatic effects than 50% of long-term type 2 patients. Despite such high of DPN on quality of life and healthcare costs, there are still no prevalence, the basic disease mechanisms of DPN are yet to be effective disease modifying treatments other than strict glycae- Corresponding author: Ria Arnold https://orcid.org/0000-0002-7469-6587 This is an Open Access article distributed under the terms of the Creative Commons Department of Exercise Physiology, School of Health Sciences, UNSW Sydney, Sydney, Attribution Non-Commercial License (https://creativecommons.org/licenses/by-nc/4.0/) NSW 2052, Australia which permits unrestricted non-commercial use, distribution, and reproduction in any E-mail: [email protected] medium, provided the original work is properly cited. Received: Dec. 8, 2021; Accepted: Feb. 25, 2022 Copyright © 2022 Korean Diabetes Association https://e-dmj.org Peripheral neuropathy in rat models of T2DM mic control and pain management. and compared measures reported using an interrupted time DPN is common in both type 1 diabetes mellitus (T1DM) series method. Measures of autonomic neuropathy were not and type 2 diabetes mellitus (T2DM), though it has long been among the key assessments of the Neurodiab guidelines and recognised they have distinct pathophysiological mechanisms thus were outside the scope of this review. Mouse models of [7-9]. The consequences of these distinct pathophysiological DPN have been reviewed elsewhere and are not consid- mechanisms were highlighted by a meta-analysis demonstrat- ered here. ing that glycaemic control, the only accepted disease modify- ing treatment, is less effective for DPN symptoms in individu- CRITERIA FOR PHENOTYPING DPN IN als with T2DM than T1DM. Research has sought to de- RODENT MODELS ACCORDING TO velop preclinical models that allow for the metabolic comor- ‘NEURODIAB’ bidities associated with T2DM to be studied, such as obesity, hypertension, dyslipidemia, inflammation, and insulin resis- Behavioural tests tance [11-13], thus requiring modifications to the high dose Currently, there is no single gold standard behavioural test to streptozotocin (STZ) model of T1DM. While rat and mouse assess neuropathy in rodent models. The behavioural test of models of T1DM and T2DM have been reviewed previously choice for small fiber neuropathy is the Hargreaves test, which [14-16], here we sought to evaluate the quality of DPN pheno- measures hindpaw withdrawal response latency when the typing, specifically in rat models of T2DM. plantar surface of a single paw is exposed to escalating heat The growth and refinement in rat T2DM models over the. Alternative behavioural measures assess tactile allodynia past 2 decades have been accompanied by an increased focus by recording hindpaw withdrawal responses in response to the on improving the consistency of protocols used to objectively application of von Frey monofilaments (or automated pressure measure and report DPN. To this end, in 2014, the Diabetic filaments) to the plantar surface, thought to provide informa- Neuropathy Study group (Neurodiab) of the European Associ- tion about large fiber dysfunction [18,19]. Including more than ation for the Study of Diabetes (EASD) established a set of one behavioural test is recommended for studying disease consensus criteria for phenotyping DPN in rodent models mechanisms and evaluating drug effects. with the intention of enabling collaboration between laborato- ries, standardising data reporting, and thus expediting the dis- Nerve conduction studies covery of effective treatments for DPN. The Neurodiab Nerve conduction studies (NCS) are the current gold standard guidelines define DPN as the presence of statistically signifi- for clinical drug trials measuring large fiber function and cant differences between diabetic and age-matched control an- should be included as an endpoint in phenotyping and screen- imals in at least two out of three measures of behaviour, nerve ing for potential therapies in diabetic rodents. The Neuro- conduction, and peripheral nerve structure. The Neurodiab diab guidelines recommend assessing nerve conduction veloc- guidelines also emphasise the importance of experimental de- ity (NCV) in both motor and sensory nerves, while controlling sign through randomisation of animals to groups, blinding of core and near-nerve temperatures, as NCVs are temperature- researchers for analyses, reporting key diabetic parameters sensitive. Assessing NCV in the caudal nerve is not strongly (e.g., weight, blood glucose, glycosylated hemoglobin, blood recommended as this is a unique anatomical feature of rodents pressure, insulin, and lipids), and reporting both positive and with less translational relevance. negative results. These guidelines focus on somatic nerves as there was insufficient data to include evaluation of autonomic Peripheral nerve structure manifestations of DPN in rodent models. Quantifying intraepidermal nerve fiber density (IENFD) in Here we review the evolution of rat T2DM models in the the foot pad of diabetic rodents is considered a reliable and study of DPN over time. We evaluated whether the publication sensitive marker of small sensory nerve fiber loss [20-22]. Sur- of the Neurodiab guidelines in 2014 influenced the reporting rogate markers of peripheral nerve structure include measures of DPN in the literature, as indicated by use of all three key of nerve trunk morphometry (large and small fibers) and cor- endpoints as recommended. To achieve this, we conducted a neal nerve fiber analysis. systematic search of rat models of T2DM that studied DPN https://e-dmj.org Diabetes Metab J 2022;46:198-221 199  Hossain MJ, et al. METHODS: LITERATURE SEARCH AND RESULTS STUDY SELECTION A scoping review was undertaken up to 3rd November 2020 Summary of included studies and evaluation of studies using the following terms: ((T2DM OR Non-insulin dependent pre- and post-publication of the Neurodiab guidelines diabetes mellitus OR diabetes mellitus type-II) AND (Neuro- Table 1 summarises the 125 articles included in this review, path* OR diabetic neuropathies OR polyneuropathies) AND which were categorized into diet and chemically induced mod- (rat OR rats)). The search terms were entered into PubMed, els (n=63) or transgenic/spontaneous models (n=62) of T2DM. Web of Science and Scopus, yielding 1,625 results. The screen- We identified three diet and chemically induced T2DM mod- ing and review procedure for these articles is shown in the flow els, the most common of which was high-fat diet (HFD) plus diagram (Fig. 1). After removal of duplicates and screening, low dose STZ in Sprague-Dawley (SD) rats (51/63 studies). Of 125 articles were included in this review for qualitative synthe- the eight transgenic/spontaneous models identified, Zucker sis. Criteria for inclusion were that the articles were in a rat diabetic fatty (ZDF) rats were most frequently studied (36/62 model of T2DM and assessed at least one of the three key DPN studies). Overall, studies employing diet and chemically in- endpoints (i.e., behavioural assessment, electrophysiology, and duced T2DM models tended to assess all three DPN endpoints nerve structure). Exclusion criteria were studies on T1DM, (19/63, 30%) more frequently than transgenic models (10/62, clinical studies, reviews, book chapters, non-rat models, non- 16%) (χ2 (1, 125)=3.45, P=0.063) (Fig. 2). Similarly, significant diabetic models, neo-natal models of T2DM, studies with no changes in at least two endpoints—meeting the Neurodiab cri- DPN endpoints, full text unavailable or not in English, confer- teria for DPN—were detected more often in diet and chemi- ence abstracts, and in vitro studies. Articles that fulfilled the cally induced models (32/63, 50.8%) than in transgenic models inclusion criteria were separated into (1) diet and chemically (24/62, 38.7%), although this difference was not statistically induced models, and (2) transgenic/spontaneous models. significant (χ2 (1, 125)=1.85, P=0.174). Records identified through database Identification searching: PubMed (n=329), Scopus (n=647), Web of Science (n=649) Total (n=1,625) Records after duplicates removed Records excluded (n=721) (n=1,031) Reasons: T1DM (n=187), clinical studies (n=125), reviews (n=136), non-rat model (n=134), Eligibility Records screened for titles and abstracts no DPN endpoints (n=129), (n=1,031) abstracts (n=7), non-English (n=3) Full-text articles excluded (n=186) Full-text articles assessed for eligibility Reasons: (n=310) T1DM (n=70), clinical studies (n=10), reviews (n=31), book chapter (n=1), T2DM but no DPN endpoints (n=49), non-diabet- ic model (n=10), neonatal T2DM model (n=3), full text unavailable (n=5), full text Eligible full text articles (n=124), Included non-English (n=2), conference abstracts manually added (n=1) (n=2), mouse model (n=1), in vitro study Total included (n=125) (n=1), duplicates (n=1) Fig. 1. Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) flow diagram showing search results and study selection. T1DM, type 1 diabetes mellitus; T2DM, type 2 diabetes mellitus; DPN, diabetic peripheral neuropathy. 200 Diabetes Metab J 2022;46:198-221 https://e-dmj.org Peripheral neuropathy in rat models of T2DM Table 1. Rat models of type 2 diabetes mellitus assessing DPN endpoints Proportion of articles assessing Articles observing significant No. of articles three DPN endpoints change in ≥2 DPN endpoints Model type included Pre-Neurodiab Post-Neurodiab Pre-Neurodiab Post-Neurodiab Diet and chemically induced models SD rat (HFD+low dose STZ) 51 7/18 12/33 10/18 13/33 Wistar rat (HFD+low dose STZ) 9 - 0/9 - 6/9 Wistar rat (STZ-NA model) 3 0/1 0/2 1/1 2/2 Total 63 7/19 12/44 11/19 21/44 Transgenic/spontaneous models ZDF rat 36 4/20 1/16 8/20 4/16 BBZDR/Wor rat 3 1/3 - 2/3 - GK rat 10 0/8 1/ 2 2/8 1/2 SDT fatty rat 5 0/3 0/2 2/3 0/2 OLETF rat 6 0/5 1/1 2/5 1/1 ZDSD-Pco 1 1/1 - 1/1 - NGR 1 - 1/1 - 1/1 WDF 1 0/1 - 0/1 - Total 63-1 a 6/41-1 a 4/22 17/41-1 a 7/22 Grand total 125 13/59 16/66 28/59 28/66 The Neurodiab guidelines were published on the 17th of June, 2014. A 12-month window was included, and thus ‘pre-Neurodiab’ refers to arti- cles published on or before 16th June 2015, and ‘post-Neurodiab’ refers to articles published from 17th June, 2015, to 3rd November 2020. DPN, diabetic peripheral neuropathy; SD, Sprague-Dawley; HFD, high-fat diet; STZ, streptozotocin; NA, nicotinamide; ZDF, Zucker diabetic fatty; BBZDR, Bio-Breeding Zucker diabetic rat; GK, Goto-Kakizaki; SDT, spontaneously diabetic Torii; OLETF, Otsuka Long-Evans Tokushi- ma Fatty; ZDSD, Zucker diabetic Sprague-Dawley; NGR, Nile grass rat; WDF, Wistar diabetic fatty. a One study was counted as both ZDF and WDF model and then subtracted from the total numbers. A dash (-) indicates no studies available. Note that in most cases, more studies reported neuropathy (at least 2 endpoints significantly different) than number of studies testing all 3 endpoints. 50 Comparing studies published pre and post the Neurodiab 40 guidelines captured a shift toward use of diet and chemically Number of papers induced models (19 studies pre-guidelines, 44 studies post- 30 guidelines) and away from transgenic/spontaneous models (40 pre-guidelines vs. 22 post-guidelines) (Fig. 2). Taken together, 20 the proportion of studies assessing all three DPN endpoints 10 has not increased appreciably since publication of the Neuro- diab guidelines (pre: 13/59, 22%; post: 16/66, 24%). Likewise, 0 the proportion of studies reporting DPN as per the Neurodiab Pre Post Pre Post Diet models Transgenic models definition (significant differences in at least two endpoints) was similar pre-publication (28/59 studies) and post-publica- Fig. 2. Graphical representation of publications examining dia- tion (28/66 studies) of the guidelines. This was also true when betic peripheral neuropathy (DPN) endpoints in diet+chemi- diet and chemically induced models and transgenic models cally induced (blue) or transgenic (orange) rat models of type 2 were considered separately. diabetes mellitus before (pre) and after (post) the publication of the Neurodiab guidelines for phenotyping DPN in 2014. Dark shading and percentage values indicate the number of studies Diet and chemically induced models that assessed 3 DPN endpoints as recommended. Purely chemically induced rodent models of diabetes have pri- https://e-dmj.org Diabetes Metab J 2022;46:198-221 201  Hossain MJ, et al. marily used alloxan and STZ, compounds toxic to pancreatic high-fat high-sugar (HFHS; 18 studies) diet, high-fat high- β-cells. While early studies modelled T1DM by administering fructose (HFHFr; five studies) diet, and unspecified diets high doses, leading to almost complete insulin deficiency and (three studies) (Table 2). The energy derived from fat varied severe hyperglycemia, subsequent work administered STZ at between 45% and 60%, and at least 18/60 studies mentioned lower doses alongside HFD exposure to model T2DM. lard as the source of fat in the diet. The duration of HFD feed- This approach seeks to model the aetiology of human T2DM, ing prior to STZ injection varied from 2 to 8 weeks (55/60 albeit more rapidly , by first inducing insulin resistance, studies), and the dose of STZ varied from 25 to 45 mg/kg with obesity and inflammation through HFD exposure, followed by the most common combination (18 studies) being 8 weeks of the partial destruction of pancreatic β-cells by low dose STZ to HFD feeding followed by a single dose of 30 mg/kg STZ. Most induce persistent hyperglycemia [14,26]. studies utilized a single STZ injection (55/60 studies). Three The present literature search identified 63 studies (2009 to studies administered weekly STZ injections of 25 mg/kg, for 2 2020) testing for a DPN phenotype in rat models of T2DM in- weeks [27-29], one study used weekly STZ injections of 30 mg/ duced by diet and chemical treatment. Most studies modelled kg, for 4 weeks (weeks 5 to 8) and another study used STZ T2DM through diet plus low-dose STZ (60/63 studies; 51 in injections of 25 mg/kg, repeated every 6 weeks from 2 to 20 SD rats and nine in Wistar rats); three combined high dose weeks (total four injections). One study tested three dif- STZ and nicotinamide (STZ/NA) administration in Wistar ferent STZ doses (30, 35, 40 mg/kg) with a single injection and rats with no diet manipulation (Table 2) [27-89]. Overall, be- concluded that 35 mg/kg was ideal for inducing T2DM as it led havioural tests were the most frequently assessed DPN end- to moderate and stable hyperglycemia with low rate of mortal- points (56/63 studies), and 31 studies measured more than one ity. Studies using two injections of 25 mg/kg reported hy- behavior. Nerve conduction was measured in 27/63 studies, perglycemia (250 to 400 mg/dL) [27-29] comparable to studies with 19 studies assessing both motor nerve conduction veloci- using a single dose, while one study using four injections of 30 ty (MNCV) and sensory nerve conduction velocity (SNCV). mg/kg reported higher blood glucose levels (>500 mg/dL) Peripheral nerve structural analyses were reported in 33/63. However, one study administering four injections of 25 studies of which 18 studies assessed IENFD, 11 studies as- mg/kg at 6 weekly intervals showed a progression from mod- sessed both IENFD and corneal nerve fiber length (CNFL) and erate glucose intolerance and insulin resistance (weeks 2 to 18) 16 studies analysed peripheral nerve histology or morphome- to frank hyperglycemia, obesity, dyslipidemia and insulin try. Below we describe the influence of diets and diabetes in- (weeks 18 to 42) and severe organ damage to pancreas, liver duction, duration of diabetes and sex differences on DPN end- and heart by weeks 42 to 56. points, methods used for behavioural tests, dichotomy in ther- The final mode of T2DM induction involved injecting NA mal sensitivity results, and directions for future studies. shortly followed by high dose STZ (STZ/NA model) [32,90]. NA, a poly (ADP-ribose) polymerase (PARP) inhibitor, is add- Diabetes induction approaches ed to mitigate the effects of STZ on pancreatic β-cells. NA pre- Of the 60 studies that combined diet manipulation and STZ to vents β-cell death caused by STZ-induced nicotinamide ade- induce T2DM, 42 were published after the Neurodiab guide- nine dinucleotide (NAD+) depletion in order to better mimic lines (Table 1), reflecting increasing interest in this model. the development of T2DM, and differentiating it from high Most of the studies (50/63) used young adult rats, identified by dose STZ induced T1DM models. The STZ-NA rat model either starting age (8 to 12 weeks, 20 studies) or weight (160 to of T2DM has been reported to lead to moderate hyperglyce- 300 g, 28 studies). Twelve studies used younger rats (