|Year : 2023 | Volume
| Issue : 5 | Page : 299-306
A nude mutant rat derived from Sprague Dawley-National Institute of Nutrition rat colony with normal thymus: A potential model for noncommunicable diseases
Satyavani Motha1, Pradeep Bhatu Patil1, Ravindar Naik Ramavat2, Srinivas Myadara1, S S. Y H. Qadri1
1 Department of Animal Facility, ICMR-National Institute of Nutrition, Hyderabad, Telangana, India
2 Department of Rodent Facility, ICMR-National Animal Resource Facility for Biomedical Research, Hyderabad, Telangana, India
|Date of Submission||27-Mar-2023|
|Date of Decision||31-Aug-2023|
|Date of Acceptance||02-Sep-2023|
|Date of Web Publication||02-Nov-2023|
Pradeep Bhatu Patil
Department of Animal Facility, ICMR-National Institute of Nutrition, Beside Tarnaka, Jamai-Osmania PO, Hyderabad - 500 007, Telangana
Source of Support: None, Conflict of Interest: None
BACKGROUND: A spontaneous mutant rat with a hairless phenotype and an intact thymus was discovered in a long-standing Sprague Dawley-National Institute of Nutrition (SD/NIN) rat colony at a national animal resource facility.
OBJECTIVE: We conducted extensive phenotypic and biochemical analyses on this mutant strain to determine its suitability as a preclinical model for immunocompetent testing in noncommunicable disease research.
MATERIALS AND METHODS: We subjected the mutant rats to strict and frequent phenotypic and genetic surveillance to accomplish this objective. The animals were assessed for food intake, body weight, blood cell profile, clinical chemistry, adipose tissue deposition, and bone mineral density (BMD) using total electrical body conductance (TOBEC) and dual-energy X-ray absorptiometry (DXA) analysis.
RESULTS: Initially, only two hairless mutant rats, a male and a female, were born from a single dam in the SD/NIN rat strain. However, the results indicate that the mutant colony propagated from these unique pups displayed distinct phenotypic features and exhibited differences in feeding behavior, weight gain, and clinical biochemistry. The food conversion rate was significantly higher in nude females (2.8-fold) while 26% lower in nude males. Both sexes of nude rats had significantly higher triglycerides and lower glucose levels in females. However, glucose levels did not change in male nude rats. Furthermore, nude female and male rats had significantly lower fat (TOBEC) and bone mineral content (DXA). Nonetheless, BMD was only slightly lower (7%–8%) compared to the heterozygous groups.
CONCLUSIONS: These findings indicate that the spontaneous mutant rat has the potential to serve as an immunopotent and modulatory testing system in pharmacokinetics/pharmacodynamics and toxicology, which can be further explored for therapeutic drug discovery.
Keywords: Dual-energy X-ray absorptiometry, nude rat, Sprague Dawley, total electrical body conductance
|How to cite this article:|
Motha S, Patil PB, Ramavat RN, Myadara S, H. Qadri S S. A nude mutant rat derived from Sprague Dawley-National Institute of Nutrition rat colony with normal thymus: A potential model for noncommunicable diseases. Indian J Pharmacol 2023;55:299-306
|How to cite this URL:|
Motha S, Patil PB, Ramavat RN, Myadara S, H. Qadri S S. A nude mutant rat derived from Sprague Dawley-National Institute of Nutrition rat colony with normal thymus: A potential model for noncommunicable diseases. Indian J Pharmacol [serial online] 2023 [cited 2023 Nov 28];55:299-306. Available from: https://www.ijp-online.com/text.asp?2023/55/5/299/389232
| » Introduction|| |
In animal models, hair can interfere with the observation of various biological processes such as blood vessels, tumors, subcutaneous cell transplantation or device implantation, and lesions. Hairless rat or mouse models are typically used for such experiments, but these models lack a complete immune system, which does not accurately mimic the patient's situation. To study immune responses in such experiments, immunocompetent nude rodents are preferred. Although such models exist in different parts of the world with various background strains, this publication focuses on describing the characteristics of nude rats established in the National Institute of Nutrition (NIN) animal facility.
The nude rat used in this study is a spontaneous mutation in the Sprague Dawley-NIN (SD/NIN) rat strain, which is a rat colony that has been maintained at the Indian Council of Medical Research (ICMR)-NIN animal facility in Hyderabad, India, for over 50 years. The mutation was discovered as a spontaneous model in the SD/NIN rat colony, and this identified population was selectively propagated and characterized over the next 50+ generations. The characteristics of the nude NIN/SD rats were analyzed in terms of growth curve and serum parameters of the liver, kidney, and metabolism to obtain baseline data for further research.
| » Materials and Methods|| |
The NIN animal facility selectively bred and housed mutant nude rats and their parents under controlled conditions. The facility maintained a fresh air supply with an air exchange cycle of 12–15 cycles/hour and controlled humidity and temperature levels between 50%–70% and 22°C–28°C, respectively. The animals were subjected to a 12-h dark and 12-h light cycle to maintain their circadian rhythms. After receiving approval from the Institutional Animal Ethics Committee (No. P40F/IAEC/NIN/11/2012), the experiment was conducted at ICMR-NIN, which is a facility authorized by CCSEA for breeding and research purposes.
The research examined male and female rats belonging to four distinct groups of SD/NIN rats. These groups comprised homozygous rats (both female and male, which were hairless), and heterozygous rats (both female and male, which had hair), designated as 'h−/−' and 'h+/−', respectively. A total of 24 rats, including 6 males and 6 females of both homozygous ('SD/NINhr−/−') and heterozygous ('SD/NINhr+/−'), were used in the study. The animals were 35 days old and observed for 90 days for feed intake and body weight gain. The rats were housed in open cages and provided water ad libitum. Feed intake was measured by offering 30 g of standard pelleted diet (18% protein content) and weighing the remaining feed the next day at the same time.
For body composition analysis, injectable anesthetics (injection ketamine and injection xylazine) were administered to the animals at a dose of 70 mg/kg and 2.5 mg/kg, respectively. Analysis was performed using total electrical body conductance (TOBEC) and dual-energy X-ray absorptiometry (DXA). TOBEC analysis was performed using the instrument “EM-SCAN” (also known as TOBEC) with the tube model “SA-3000” from TOBEC (Multidetector, Springfield, III, USA) to scan the animals in this study. This approach is noninvasive and measures several parameters such as fat-free mass (FFM), total fat percentage (Fat%), total body sodium (TBNa), total body potassium (TBK), and total body water (TBW). The animals were stabilized with chemical sedation prior to body composition testing. Mathematical calculations were used to determine the body composition parameters. The DXA scan was performed using the “Hologic Discovery Wi” bone densitometer, which provides data on anatomy, bone density/content, and lean mass.
Afterward, the experimental rats had blood samples extracted from the retro-orbital sinus to conduct a complete blood count and plasma analysis. The plasma was evaluated for liver-specific markers (albumin, total protein [TP], and bilirubin [BIL]), kidney-specific markers (creatinine and urea), obesity-related/metabolic disorder markers (total cholesterol [TC], triglycerides, and glucose), and tissue damage-specific enzymes (ALT-alanine transaminase/SGPT-serum glutamate pyruvate transaminase, AST-aspartate transaminase/SGOT-serum glutamate oxalate transaminase, and alkaline phosphatase [ALP]) using ACE Alera® (Clinical Chemistry System). The study was concluded by euthanizing all 24 rats through CO2 asphyxiation, followed by gross examinations and organ removal for histopathological evaluations. The data analysis was performed using GraphPad Prism, applying a one-way ANOVA followed by Tukey's post hoc test to compare the groups.
| » Results|| |
During necropsy, both homozygous and heterozygous rats had a thymus of the same size, which is in contrast to previous findings in nude rats. In brief, fluorescence-activated cell sorting (FACS) analysis revealed that the fluorescence intensity of CD4 and CD8 cells associated with the T-cell receptor complex concerning the hairless mutant rat showed no significant cell differences between the two phenotypes. There were no significant changes in the other organs. The study also compared the body composition and feed intake of nude rats with heterozygous rats. The feed intake was higher in nude rats than in heterozygous rats, and the body weight was also higher in the former. Feed intake increased until day 63 in both nude rats and heterozygous rats of both sexes. The mean food intake was higher in nude rats but lower in heterozygous rats, and the feed conversion ratio was higher in nude rats. However, the body weight of all groups increased until 63 days of age and remained stable thereafter, but adult males had a higher weight than females [Figure 1]a, [Figure 1]b, [Figure 1]c, [Figure 1]d, [Figure 1]e, [Figure 1]f. The feed conversion ratio was also higher in nude rats, indicating a higher metabolic rate [Figure 2]. Both phenotypes showed similar fertility and fecundity. Serum biochemistry markers showed high albumin levels in female nude rats, while male nude rats had slightly lower levels of TP and BIL. There were no major changes in creatinine (CRE), electrolytes, and glucose [Figure 3] and [Figure 4]. In addition to the above, body composition was assessed using DXA [Figure 5] and TOBEC [Figure 6]. Interestingly, the results indicate that fat percentage and bone mineral content (BMC) were lower in nude rats compared to heterozygous rats.
|Figure 1: Foot intake and body weight (fold increase) in homozygous (nude) animals in comparison to Sprague Dawley-National Institute of Nutrition hr+/− (Heterozygous rat), (a) Foot intake of rats in grams (mean ± standard deviation [SD]), (b) weekly feed intake in male rats, (c) weekly feed intake in female rats, (d) body weight of rats in grams (Mean ± SD), (e) weekly body weight in male rats, (f) weekly body weights female rats|
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|Figure 2: Foot conversion ratio (fold increase) in homozygous (nude) animals in comparison to Sprague Dawley-National Institute of Nutrition hr+/− (heterozygous rat). (a) Food conversion rate (FCR) in male rats, (b) FCR in female rats|
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|Figure 3: Serum markers (fold increase) in homozygous (nude) animals in comparison to Sprague Dawley-National Institute of Nutrition hr+/− heterozygous rat. (a) Liver markers in male rats, (b) liver markers in female rats, (c) kidney markers in male rats, (d) kidney markers in female rats. TP: Total protein, BIL: Bilirubin, CRE: Creatinine|
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|Figure 4: Metabolic and enzymatic markers (fold increase) in homozygous (nude) animals in comparison to Sprague Dawley-National Institute of Nutrition hr+/− heterozygous rat, (a) Metabolic markers in male rats, (b) metabolic markers in female rats, (c) enzymatic markers in male rats, (d) enzymatic markers in female rats. TC: Total cholesterol, AST: Aspartate transaminase, ALT: Alanine transaminase, ALP: Alkaline phosphatase|
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|Figure 5: Dual-energy X-ray absorptiometry analysis (fold increase) in homozygous (nude animals) in comparison with respective sex of Sprague Dawley-National Institute of Nutrition hr+/− (heterozygous) rat. (a) fat and lean body mass in male rats, (b) fat and lean body mass in female rats, (c) bone mineral density and content in male rats, (d) bone mineral density and content in female rats. Fat%: Total fat percentage, LBM: Lean body mass, BMD: Bone mineral density, BMC: Bone mineral content|
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|Figure 6: Total electrical body conductance analysis (fold increase) in homozygous (nude animals) in comparison to Sprague Dawley-National Institute of Nutrition hr+/− (heterozygous) rat. (a) Lean body mass, fat-free mass, and fat in male rats, (b) lean body mass, fat-free mass, and fat in female rats, (c) total body water, sodium, and potassium in male rats, (d) total body water, sodium, and potassium in male rats, (e) differential blood count, (f) blood count. FFM: Fat-free mass, Fat%: Total fat percentage, LBM: Lean body mass, TBK: Total body potassium, TBNa: Total body sodium, TBW: Total body water|
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The analysis of the variables revealed several significant differences. Nude females had significantly lower serum glucose levels (93 mg/dL) compared to nude males (120.6 mg/dL) (P = 0.0286). Heterozygous males exhibited significantly higher TP levels (6.825 g/dL) compared to heterozygous females (6.310 g/dL) (P = 0.0231). In terms of total triglycerides, nude females had significantly lower levels (27.33 mg/dL) compared to heterozygous females (35.33 mg/dL) (P = 0.0119), while nude males had significantly lower levels (26.20 mg/dL) compared to heterozygous females (P = 0.0060).
Moreover, nude females had significantly higher serum urea levels (47.33 mg/dL) compared to heterozygous males (34.00 mg/dL) (P = 0.0092). Both phenotypic females, whether nude (73.83 mg/dL) or heterozygous (71.17 mg/dL), had significantly higher TC levels compared to males, whether nude (56.20 mg/dL) or heterozygous (56.33 mg/dL) (P < 0.0001).
In addition, no significant changes were observed in the levels of BIL, albumin, ALP, SGPT, SGOT, and creatinine among the different groups. Furthermore, FAC analysis revealed no changes in the percentage of CD4 and CD8 cell populations in both phenotypes.
In summary, the findings consistently indicate that nude females have lower serum glucose levels, lower total triglyceride levels, and higher serum urea levels compared to other groups. Heterozygous males exhibit higher TP levels, while both phenotypic females have higher TC levels. In terms of food intake, nude females tend to consume less food, while nude males and normal females consume more. Normal males fall in between. It is important to note that there were no significant differences in weight gain at various time points during the growth period, except at day 84, where heterozygous females had a significantly higher weight gain compared to males.
| » Discussion|| |
Foxn1, also known as the “nude” gene, has been extensively studied for its ability to induce the nude phenotype. When this gene undergoes mutations or alterations, it disrupts the normal development and functioning of the thymus gland. As a consequence, individuals with such mutations lack the capacity to produce T-cells efficiently. This genetic model has significantly contributed to our understanding of immunology, transplantation, and various disease mechanisms, making it an indispensable tool in scientific research,, here in our nude phenotype rat model we are yet to confirm the mutation in Foxn1. However, it is known that it affects the thyroid gland and thereby depletes T-cells; however, in our nude rat model, we did not find any change in the T-cell population; therefore, it was not checked yet. Likewise, additional reports propose that congenital alterations are accountable for the presence of T-cells in certain nude rats., Biochemical parameters were relatively at the higher end compared to athymic nude rats.
During necropsy, the thymus was found to be present in both SD/NIN rats (hr−/− and hr+/−), in contrast to the previous literature which described nude rats., The absence of significant alterations in the remaining organs, along with supporting FACS data (which is currently unpublished), renders this model advantageous for research studies that necessitate a robust immune response and require the animals to be housed in a barrier-free environment.
Regarding feed intake and body weight, both homozygous (nude rats) and heterozygous rats of both sexes exhibited a gradual increase in feed intake until day 63rd (9 weeks) [Figure 1]a. After the 9th week, the mean food intake was higher in nude rats (22.53 g/day for females and 27.47 g/day for males), while it was lower in heterozygous rats (16.52 g/day for females and 20.12 g/day for males) [Figure 1]b and [Figure 1]c. In comparison, feed intake was 36% higher in both male and female nude rats compared to heterozygous rats. In addition, protein concentration also had an impact on the amount of feed intake. In general, an adult laboratory rat receives 15 g of feed per day for maintenance, 15–20 g per day during gestation, and 30–40 g per day during lactation.
The TOBEC technique was used to assess body composition at various time points after 3 months of age, alongside DXA. In comparison to heterozygous rats, female nude rats showed a low-fat percentage of 37% in the TOBEC analysis, whereas male rats had a low-fat percentage of 31% [Figure 6]a and [Figure 6]b. The FFM and lean body mass (LBM) did not change significantly (1.05-fold and 1.03-fold, respectively) between nude and heterozygous female rats, but the percentage of fat was lower (0.63-fold) in nude female rats.
Furthermore, the percentage of TBK, TBNa, and TBW was extrapolated from an e-value of TOBEC, and no significant differences were observed between nude female rats (1.05-fold, 1.05-fold, and 1.05-fold, respectively) and heterozygous female rats [Figure 6]d. Similarly, there were no significant differences observed in FFM% (1.04-fold) and LBM% (1.03-fold) between male nude and heterozygous rats, but the fat percentage was lower in nude male rats (0.69-fold). In addition, the electrolytes (TBK and TBNa) and water content (TBW) were similar in nude (1.04, 1.04, and 1.01, respectively) and male NIN/SD rats [Figure 6]c.
Using DXA for body composition analysis, a week after TOBEC, it was found that the nude rats (both females and males) had a slightly reduced fat percentage [Figure 5]a and [Figure 5]b, while their LBM remained unchanged (female: 1.06-fold, male: 1.02-fold). In addition, the DXA analysis showed lower BMC (female: 0.79-fold, male: 0.76-fold) and bone mineral density (BMD) (female: 0.93-fold, male: 0.92-fold) in the nude rats [Figure 5]c and [Figure 5]d. The feeling of cold on bare skin generally requires the burning of fat, particularly brown fat, to generate more energy. However, certain animals like the nude mole rat have developed the ability to reduce energy requirements by enduring hypoxia to anoxia for up to 3 h.
The serum biochemistry markers revealed interesting gender-based differences in nude rats. Females showed a significant increase in albumin levels (1.29-fold), while males exhibited no such change (0.98-fold). Interestingly, TP and BIL remained unaffected in nude females (1.01-fold and 1.02-fold, respectively), while males had slightly lower levels of TP (0.92-fold) and BIL (0.91-fold) compared to heterozygous male rats [Figure 3]a and [Figure 3]b. Surprisingly, CRE levels did not show significant changes in either female (0.93-fold) or male (0.96-fold) nude rats. However, urea levels were increased in both female (1.20-fold) and male (1.12-fold) nude rats compared to their counterparts in heterozygous rats of each gender [Figure 3]c and [Figure 3]d.
In female nude rats, glucose levels were significantly low (0.77-fold), while male nude rats showed no significant change (1.04-fold). Interestingly, TC levels were markedly high in both female (1.31-fold) and male (1.26-fold) nude rats, while serum triglycerides showed no significant changes (female: 1.04-fold, male: 1.08-fold) [Figure 4]a and [Figure 4]b. Notably, albumin levels were high (29%) in nude females, as was blood urea (20%), while CRE (a renal marker) showed minimal changes. The ratio of urea to albumin was also not significantly different, whether in nude females (11.8) or males (10.2) or heterozygous rats (females: 10.3, males: 8.87).
In comparison to heterozygous rats, both male and female nude animals exhibited higher levels of TC. However, in female nude animals, glucose levels were 23% lower, which may help to hinder further cholesterol deposition. Some studies suggest that elevated glucose levels can impact cholesterol transport and metabolism, whereas high cholesterol levels can alter glucose metabolism in return. Despite having a high feed intake, nude female animals maintained low glucose levels and weight, which is surprising and requires further investigation. While numerous studies have linked blood glucose levels to cholesterol levels,, the nude animals in this study seem to possess a mechanism that challenges this hypothesis.
In addition, triglyceride levels were normal in both sexes of nude rats, possibly due to the high energy requirements of glucose consumption that prevent triglyceride deposition or keep them at a normal level, allowing this model to control glucose effectively.
AST liver enzymes showed no significant changes [Figure 4]c and [Figure 4]d between NIN/SD rats and nude animals (female: 1.02-fold, male: 0.98-fold). However, ALT was lower in nude rats (female: 0.87-fold, male: 0.84-fold), which can be caused by factors such as lower muscle mass. It should be noted that a decrease in ALT does not necessarily indicate a negative health condition.
Furthermore, the enzyme ALP, which is related to bone metabolism, was found to decrease in male nude rats (0.79-fold) but not in female nude rats (0.96-fold). This reduction in ALP levels corresponds with the DXA results showing low BMC and BMD in male nude rats, but not in females. The discrepancy in females could be due to several factors, including multiple myeloma and osteoporosis.
In addition, it is possible that low ALP values in male nude rats could be due to protein deficiency (malnutrition) as they consumed less food than females, although there was no correlation found in TOBEC and DXA (FFM% and LBM% were normal).
The results of the hematological profile showed no changes in the absolute numbers of platelets, erythrocytes, and white blood cells [Figure 6]. However, the nude rats exhibited a higher number of monocytes and a lower number of eosinophils at 1.10-fold and 0.78-fold, respectively. It is important to note that the increase in monocytes may indicate various pathologies, such as chronic infections, chronic stress on the kidney, an immunosuppressed state, autoimmune diseases, chronic viral diseases, and cancer-related conditions.
The nude rat from the SD/NIN colony displays unique alterations in blood, serum, fat, and bone parameters, making it an excellent candidate for a genetic model in nutritional research. A thorough investigation is required to better comprehend the mechanisms and physiology of nude animals. This model can be utilized for wound healing, topical toxicity testing, and other research involving the interaction between skin and nutrition.
| » Conclusions|| |
Our model does not require a barrier facility, unlike the immunocompromised animals, making it suitable for a range of studies without the need for specialized infrastructure or housing to address morbidity or mortality concerns. In addition, the nude animal model we offer at our facility is highly resilient, and its distinctive blood profile and excellent feed conversion can prove advantageous in nutritional research.
Further examination is necessary to determine the specific fat type present in our model, conduct behavioral tests, and assess its susceptibility to cancer or metabolic disease. A comprehensive understanding using meta-genomics could offer potential solutions to malnutrition issues.
We would like to thank Ms. T. Lalitha, Mr. Saida D., and Mr. Harinarayana for their constant support in animal experiments.
Financial support and sponsorship
The authors would like to thank the Indian Council of Medical Research (ICMR) and the ICMR-National Institute of Nutrition, Government of India, for funding this study. (Grant No. 13-NC-01).
Conflicts of interest
There are no conflicts of interest.
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