2022 White Paper on Recent Issues in Bioanalysis: FDA Draft Guidance on Immunogenicity Information in Prescription Drug Labeling, LNP & Viral Vectors Therapeutics/Vaccines Immunogenicity, Prolongation Effect, ADA Affinity, Risk-based Approaches, NGS, qPCR, ddPCR Assays (Part 3 - Recommendations on Gene Therapy, Cell Therapy, Vaccines Immunogenicity & Technologies; Immunogenicity & Risk Assessment of Biotherapeutics and Novel Modalities; NAb Assays Integrated Approach)

The 2022 16th Workshop on Recent Issues in Bioanalysis (WRIB) took place in Atlanta, GA, USA on September 26-30, 2022. Over 1000 professionals representing pharma/biotech companies, CROs, and multiple regulatory agencies convened to actively discuss the most current topics of interest in bioanalysis. The 16th WRIB included 3 Main Workshops and 7 Specialized Workshops that together spanned 1 week in order to allow exhaustive and thorough coverage of all major issues in bioanalysis, biomarkers, immunogenicity, gene therapy, cell therapy and vaccines. Moreover, in-depth workshops on ICH M10 BMV final guideline (focused on this guideline training, interpretation, adoption and transition); mass spectrometry innovation (focused on novel technologies, novel modalities, and novel challenges); and flow cytometry bioanalysis (rising of the 3rd most common/important technology in bioanalytical labs) were the special features of the 16th edition. As in previous years, WRIB continued to gather a wide diversity of international, industry opinion leaders and regulatory authority experts working on both small and large molecules as well as gene, cell therapies and vaccines to facilitate sharing and discussions focused on improving quality, increasing regulatory compliance, and achieving scientific excellence on bioanalytical issues. This 2022 White Paper encompasses recommendations emerging from the extensive discussions held during the workshop and is aimed to provide the bioanalytical community with key information and practical solutions on topics and issues addressed, in an effort to enable advances in scientific excellence, improved quality and better regulatory compliance. Due to its length, the 2022 edition of this comprehensive White Paper has been divided into three parts for editorial reasons. This publication (Part 3) covers the recommendations on Gene Therapy, Cell therapy, Vaccines and Biotherapeutics Immunogenicity. Part 1 (Mass Spectrometry and ICH M10) and Part 2 (LBA, Biomarkers/CDx and Cytometry) are published in volume 15 of Bioanalysis, issues 16 and 15 (2023), respectively.

Identification of SARS-CoV-2 variants using viral sequencing for the Centers for Disease Control and Prevention genomic surveillance program

BACKGROUND

The Centers for Disease Control and Prevention contracted with laboratories to sequence the SARS-CoV-2 genome from positive samples across the United States to enable public health officials to investigate the impact of variants on disease severity as well as the effectiveness of vaccines and treatment. Herein we present the initial results correlating RT-PCR quality control metrics with sample collection and sequencing methods from full SARS-CoV-2 viral genomic sequencing of 24,441 positive patient samples between April and June 2021.

METHODS

RT-PCR confirmed (N Gene Ct value < 30) positive patient samples, with nucleic acid extracted from saliva, nasopharyngeal and oropharyngeal swabs were selected for viral whole genome SARS-CoV-2 sequencing. Sequencing was performed using Illumina COVIDSeq™ protocol on either the NextSeq550 or NovaSeq6000 systems. Informatic variant calling, and lineage analysis were performed using DRAGEN COVID Lineage applications on Illumina's Basespace cloud analytical system. All sequence data and variant calls were uploaded to NCBI and GISAID.

RESULTS

An association was observed between higher sequencing coverage, quality, and samples with a lower Ct value, with < 27 being optimal, across both sequencing platforms and sample collection methods. Both nasopharyngeal swabs and saliva samples were found to be optimal samples of choice for SARS-CoV-2 surveillance sequencing studies, both in terms of strain identification and sequencing depth of coverage, with NovaSeq 6000 providing higher coverage than the NextSeq 550. The most frequent variants identified were the B.1.617.2 Delta (India) and P.1 Gamma (Brazil) variants in the samples sequenced between April 2021 and June 2021. At the time of submission, the most common variant > 99% of positives sequenced was Omicron.

CONCLUSION

These initial analyses highlight the importance of sequencing platform, sample collection methods, and RT-PCR Ct values in guiding surveillance efforts. These surveillance studies evaluating genetic changes of SARS-CoV-2 have been identified as critical by the CDC that can affect many aspects of public health including transmission, disease severity, diagnostics, therapeutics, and vaccines.

Centralisation of rectal cancer care has improved patient survival in the republic of Ireland

BACKGROUND

Centralisation of rectal cancer surgery to designated centres was a key objective of the Irish national cancer control program. A national audit of rectal cancer surgery indicated centralisation was associated with improved early surgical outcomes. This study aimed to determine the impact of implementation of the national cancer strategy on survival from rectal cancer.

MATERIALS AND METHODS

Data were collected from the National Cancer Registry of Ireland to include all patients with Stage I-III rectal cancer undergoing rectal cancer surgery with curative intent between 2003 and 2012. Five-year overall survival and cancer-specific survival was compared between patients in the pre-centralisation (2003-2007) and post-centralisation period (2008-2012) and between patients receiving surgery in designated cancer centres and non-cancer centres.

RESULTS

The proportion of rectal cancer surgery performed in a designated cancer centre increased from 42% during 2003-2007 to 58% during 2008-2012. Five-year overall survival increased from 66.1% in 2003-2007 to 73.5% in 2008-2012 (p < 0.001). Five-year cancer-specific survival increased from 75.3% in 2003-2007 to 81.9% in 2008-2012 (p < 0.001). Surgery in a cancer centre and surgery post-centralisation were significantly associated with overall and cancer specific survival using Cox proportional hazards regression.

CONCLUSION

Survival following resection of rectal cancer was significantly improved following implementation of a national cancer strategy incorporating centralisation of rectal cancer surgery.

Visual-vestibular processing deficits in mild traumatic brain injury

BACKGROUND

The search for reliable and valid signs and symptoms of mild traumatic brain injury (mTBI), commonly synonymous with concussion, has lead to a growing body of evidence that individuals with long-lasting, unremitting impairments often experience visual and vestibular symptoms, such as dizziness, postural and gait disturbances.

OBJECTIVE

Investigate the role of visual-vestibular processing deficits following concussion.

METHODS

A number of clinically accepted vestibular, oculomotor, and balance assessments as well as a novel virtual reality (VR)-based balance assessment device were used to assess adults with post-acute concussion (n = 14) in comparison to a healthy age-matched cohort (n = 58).

RESULTS

Significant between-group differences were found with the VR-based balance device (p = 0.001), with dynamic visual motion emerging as the most discriminating balance condition. The symptom reports collected after performing the oculomotor and vestibular tests: rapid alternating horizontal eye saccades, optokinetic stimulation, and gaze stabilization, were all sensitive to health status (p < 0.05), despite the absence of oculomotor abnormalities being observed, except for near-point convergence. The BESS, King-Devick, and Dynamic Visual Acuity tests did not detect between-group differences.

CONCLUSION

Postural and visual-vestibular tasks most closely linked to spatial and self-motion perception had the greatest discriminatory outcomes. The current findings suggest that mesencephalic and parieto-occipital centers and pathways may be involved in concussion.

Smoking at diagnosis significantly decreases 5-year cancer-specific survival in a population-based cohort of 18 166 colon cancer patients

BACKGROUND

Accumulating evidence suggests smoking may adversely affect cancer patients' outcomes. Previous studies of smoking and survival in colon cancer have been limited by size and/or lack of a population basis and results have been inconsistent.

AIM

To investigate in a large population-based cohort whether smoking status at diagnosis is an independent prognostic factor for cancer-specific survival in colon cancer and whether treatment modifies any impact of smoking.

METHODS

Colon adenocarcinomas diagnosed between 1994 and 2012 were abstracted from the National Cancer Registry Ireland, and classified by smoking status at diagnosis. Cancer-specific death rates over 5 years were compared in current, ex- and never smokers using multivariable Cox proportional hazards models, and subgroup analyses by treatment (combinations of cancer-directed surgery and chemotherapy) were conducted.

RESULTS

Of 18 166 colon cancers, 20% of patients were current smokers, 23% ex-smokers and 57% never smokers. Compared to never smokers, current smokers had a significantly raised cancer death rate [multivariable hazard ratio (HR) = 1.14, 95% CI: 1.07-1.12]. There was a significant interaction between treatment and smoking (P = 0.03). In those who had cancer-directed surgery only, but not other groups, current smokers had a significantly increased cancer death rate compared to never smokers (HR = 1.21, 95% CI: 1.09-1.34).

CONCLUSIONS

Smoking at diagnosis is an independent prognostic factor for colon cancer. The limitation of the association to surgically-treated patients suggests that the underlying mechanism(s) may be related to surgery. While further research is needed to elucidate mechanisms, continued efforts to encourage smoking prevention and cessation may yield benefits in terms of improved survival from colon cancer.

Colorectal cancer incidence and survival by sub-site and stage of diagnosis: a population-based study at the advent of national screening

BACKGROUND

The location and staging of a colorectal cancer (CRC) determine prognosis and choice of treatment. We examined the sub-site, sex, and stage distribution for CRC in Ireland for patients diagnosed in the period immediately prior to the implementation of a national screening programme.

METHODS

Incident cases of CRC were abstracted from the National Cancer Registry for the period 1994-2012 (n = 38,912). Incidence proportions and 3-year cancer-related survival were calculated.

RESULTS

The incidence of CRC during 2010-2012 averaged 1021 females and 1424 males per year. While the overall incidence rate of CRC was static during 1994-2012, this masked a significant increase in the rate of proximal colon tumours (+1.3 % per year), a decreases in the rate of tumours of overlapping/colon NOS (-2.2 % per year), and no change in the rates of cancers of the distal colon and rectosigmoid junction (RSJ)/rectum. Proximal tumours occurred more frequently in females (F vs. M, 38 vs. 29 %), in older persons and increased over time. Compared to distal colon tumours, proximal colon [RR risk ratio 1.08, 95 % CI (1.05, 1.10)] and RSJ/rectum tumours [RR 1.08 (1.05, 1.11)] were more likely to be diagnosed at late stage. The proportion of late-stage tumours increased steadily over five diagnosis periods [e.g., 1994-1997 (51 %) vs. 2010-2012 (57 %), RR 1.12 (1.08, 1.16)]. Cancer survival improved over four diagnosis periods.

CONCLUSIONS

There was a distal-to-proximal shift and a trend towards diagnosis at late stage during 1994-2012. Some reversal of this trend is expected following the implementation of a national screening programme.

Salivary and serum adiponectin and C-reactive protein levels in acute myocardial infarction related to body mass index and oral health

BACKGROUND AND OBJECTIVE

Adiponectin is produced by adipose cells and is considered an anti-inflammatory molecule. In contrast, C-reactive protein (CRP) has been identified as a hallmark of systemic inflammation and used as a risk marker of cardiovascular disease (CVD). Of interest was the relationship of these two biomarkers to oral health and CVD risk.

MATERIAL AND METHODS

This investigation examined these two molecules in serum and unstimulated whole saliva of patients within 48 h of an acute myocardial infarction (AMI) compared to control subjects. We hypothesized a differential response in these biomolecules resulting from the heart attack that would be affected by both the body mass index and oral health characteristics of the individuals.

RESULTS

Significantly lower adiponectin levels were observed in the serum of patients with AMI. Serum adiponectin in both groups and salivary adiponectin in patients with AMI decreased with increasing body mass index. Oral health was significantly worse in patients with AMI, and both serum and salivary adiponectin were elevated with better oral health in control subjects. Serum CRP levels were increased in patients with AMI regardless of their oral health, and both serum and salivary CRP were significantly elevated in S-T wave elevated patients with MI.

CONCLUSIONS

These initial data provide evidence relating obesity and oral health to salivary and serum analyte levels that occur in association with cardiac events. Relationships have been described between CVD risk and periodontal disease. Additionally, various systemic inflammatory biomarkers appear to reflect both the CVD risk and the extent/severity of periodontitis. Our findings indicated that oral health and obesity contribute to altering levels of these salivary and serum analytes in association with cardiac events. The potential that serum and/or salivary biomarkers could aid in evaluating CVD risk requires knowledge regarding how the oral health of the individual would impact the effectiveness of these biological measures.

Programmable bio-nanochip-based cytologic testing of oral potentially malignant disorders in Fanconi anemia

Fanconi anemia (FA) is caused by mutations of DNA repair genes. The risk of oral squamous cell carcinoma (OSCC) among FA patients is 800-folds higher than in the general population. Early detection of OSCC, preferably at it precursor stage, is critical in FA patients to improve their survival. In an ongoing clinical trial, we are evaluating the effectiveness of the programmable bio-nanochip (p-BNC)-based oral cytology test in diagnosing oral potentially malignant disorders (OPMD) in non-FA patients. We used this test to compare cytomorphometric and molecular biomarkers in OSCC cell lines derived from FA and non-FA patients to brush biopsy samples of a FA patient with OPMD and normal mucosa of healthy volunteers. Our data showed that expression patterns of molecular biomarkers were not notably different between sporadic and FA-OSCC cell lines. The p-BNC assay revealed significant differences in cytometric parameters and biomarker MCM2 expression between cytobrush samples of the FA patient and cytobrush samples of normal oral mucosa obtained from healthy volunteers. Microscopic examination of the FA patient's OPMD confirmed the presence of dysplasia. Our pilot data suggests that the p-BNC brush biopsy test recognized dysplastic oral epithelial cells in a brush biopsy sample of a FA patient.

Factors affecting receipt of a medical card in a cohort of colorectal cancer patients, 2002-2006

The criteria for allocation of medical cards to colorectal cancer patients < 70 were explored. All invasive colorectal cancers diagnosed during 2002-2006 (n = 4,762) were abstracted and linked to the PCRS master file to determine medical card status. Determinants of medical card possession before diagnosis were; age 65-69yr vs. 15-54 yr (OR = 3.95 (95% CI); 3.20-4.88), other status vs. married (OR = 1.89; 1.61-2.23), most vs. least deprived (OR = 3.65; 2.89-4.61), smoker vs. non-smoker (OR = 1.98; 1.64-2.37), ED population density (< 1/ha vs. > 15/ha; OR = 1.47; 1.20-1.80). Determinants of medical card possession after diagnosis were; age 65-69 yr vs. 15-54 yr (OR = 0.77; 0.62-0.96), most vs. least deprived (OR = 2.15; 1.72-2.70), stage IV vs. 1: OR = 2.49; 1.85-3.36), chemotherapy (OR = 2.30; 1.87-2.83), radiotherapy (OR = 1.40; 1.13-1.72), ED population density (< 1/ha vs. > 15/ha; OR = 1.47; 1.19-1.82), HSE South vs. DNML (OR = 1.76; 1.40-2.21). Medical card possession among colorectal cancer patients was determined by greater age and deprivation before diagnosis; and younger age, greater deprivation, advanced stage and treatments warranted by extent of disease after diagnosis. Low population density of ED of residence also predicted card receipt.

A dose-escalating phase I study of biweekly docetaxel in older men with hormone refractory prostate cancer (HRPC)

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Background: Docetaxel has been shown to be effective and is used in the treatment of HRPC. This phase I study is designed to investigate the maximum tolerated dose, tolerability and activity of docetaxel administered on a biweekly schedule in older patients with HRPC. This study will also explore the feasibility of a self-report geriatric assessment tool in this population. Methods: HRPC patients with progression of metastatic disease during hormonal therapy received docetaxel q 2 wks at dose levels of 40 (level 0), 45 (level 1), 50 (level 2), or 55 mg/m2 (level 3). The trial is a conventional phase I 3+3 dose-escalation design. Treatment was continued until progression, refused further treatment, or unacceptable toxicity. Patients were given the Vulnerable Elders Survey (VES-13) for completion every 4 weeks. Results: 16 patients were enrolled in the study. All are evaluable for toxicity, 10 for response. Pts had a median (range) age 76 (72–87). Median doses administered was 6 (range 3–19). The maximum tolerated dose (MTD) was not reached in the study. No dose limiting side effects were reported for any of the dosing levels in the 8 week assessment period. Five patients had a ≥50% decline in serum PSA on two consecutive measurements taken at least 2 weeks apart. Of the 10 patients with measureable disease, 2 patients (one at dose level 0 and one at dose level 3) achieved a complete response, 2 patients (one at dose level 1 and one at dose 2) achieved a partial response, and 3 patients had stable disease (one each at dose levels 1, 2, and 3). At the time of entry onto the study, 4 patients required narcotic analgesics for bone pain; after treatment, 1 (25%) discontinued their pain medications. The completion rate of the Vulnerable Elders Survey (VES-13) was 94.6%. Conclusions: Biweekly docetaxel can be safely administered in older metastatic HRPC patients and showed activity. For phase II evaluation, a bi-weekly dose of 55 mg/m2 appears to be suitable. The administration of the VES-13 was feasible in this population.

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Tyrosine phosphorylation in the human duodenum

Many growth factor receptors including the epidermal growth factor receptor function through tyrosine kinase activity. The aim of this study was to examine the constitutive level of tyrosine phosphorylation in the normal duodenum and in the hyperproliferative coeliac duodenum. A flow cytometric assay was devised using monoclonal antibody to phosphorylated (but not native) tyrosine residues to determine the levels of tyrosine phosphorylation in both CD3 positive intraepithelial lymphocytes and CD3 negative epithelial cells obtained by EDTA treatment of endoscopically obtained duodenal biopsy specimens. In addition, immunohistochemistry was performed on 18 formalin fixed coeliac duodenal biopsy specimens and eight control specimens. Tyrosine phosphorylation could be detected by flow cytometry on duodenal enterocytes and this expression was up regulated by pretreatment with epidermal growth factor. Tyrosine phosphorylation decreased with progression from the villus to the crypt, however, and was virtually undetectable on crypt enterocytes. Immunohistochemistry of the coeliac duodenum showed virtually absent tyrosine phosphorylation in the crypt. Increased tyrosine phosphorylation was detected in the infiltrating T cells. In conclusion, tyrosine phosphorylation in the duodenum is confined to the non-proliferative villous epithelium and is virtually undetectable in the proliferative crypt compartment. These findings suggest that tyrosine kinase activity is not a significant factor in the regulation of crypt cell proliferation in the human duodenum either in normal subjects or in coeliac disease patients.

Gastric T lymphocyte responses to Helicobacter pylori in patients with H pylori colonisation

Helicobacter pylori has been identified as a dominant factor in the pathogenesis of duodenal ulcer. The aim of this study was to examine peripheral blood and gastric lymphocyte proliferation and cytokine production in patients with H pylori colonisation. Sixty five dyspeptic patients attending for endoscopy were studied; 35 of these were H pylori positive and 30 H pylori negative as assessed by culture, histology, and rapid urease test. H pylori antigen was capable of stimulating peripheral blood lymphocyte proliferative responses even in H pylori negative patients. Peripheral blood lymphocyte proliferative responses to H pylori (but not to purified protein derivative or phythaemagglutinin) were significantly lower in H pylori positive than H pylori negative patients. Similarly, antigen specific proliferative responses and interferon gamma production by gastric lamina propria lymphocytes were also depressed in H pylori positive patients compared with H pylori negative patients. CD8 and CD22 positive lamina propria lymphocytes were increased in H pylori positive patients. These data show that antigen specific responses to H pylori are significantly lower in H pylori positive patients and could indicate activation of antigen specific suppression.

Changes in immunological parameters during interleukin 2 and interferon 2 alpha treatment of recurrent renal cell carcinoma and malignant melanoma

Immunological parameters were studied in patients with either advanced renal cell cancer (n = 7) or advanced malignant melanoma (n = 6) during treatment with a low-dose continuous intravenous treatment with human recombinant interleukin-2 (hr IL-2) and recombinant interferon alpha-2a. Before treatment, natural killer (NK) cell activity was found to be significantly lower in these patients than in 10 normal controls. However, the numbers of NK cells in circulation were equivalent; following incubation of the patients' peripheral blood mononuclear cells (PBMC) with IL-2 for three days normal lymphokine activated killer (LAK) cell activities were induced. Thus, in-vitro incubation with IL-2 appeared to overcome a defect in NK activity. We next examined the effect of IL-2/IFN alpha therapy on in-vitro LAK induction. Treatment significantly increased in-vitro LAK activity in eight of nine patients tested, although in-vivo LAK cell activity was not altered during treatment. The numbers of NK cells (CD16+ CD56+) in peripheral blood showed a significant increase in seven of ten patients as a result of treatment. The three patients who showed the best clinical response also showed the highest increase in expression of these phenotypic markers. T cells were found to be activated in 8/10 patients as indicated by increased co-expression of CD3 with CD25 after completion of 4-day continuous intravenous infusion of IL2. Four days before the start of treatment, cancer patient PBMC stimulated with concanavalin A (con A) produced significantly greater amounts of TNF compared to normal controls. In-vitro inducible TNF was found to decrease following treatment. Since IL-2 production and lymphocyte proliferation in response to Con A were normal in the patient group and were not altered by treatment, the reduction in TNF levels seemed not to be a general inhibitory effect. Further study of these and other changes in the immune system during IL-2/IFN alpha treatment may help to understand how these immunoregulators cause tumour destruction and to predict their usefulness in individual patients.

A phase 2 trial of recombinant interleukin-2 and 5-fluorouracil in patients with metastatic colorectal carcinoma

The toxicity and efficacy of sequential 5-fluorouracil (5-FU) and recombinant interleukin-2 (IL-2) were evaluated in 12 patients with metastatic colorectal carcinoma. This combination of 5-FU and IL-2 produced a 10% partial response rate with 40% of patients remaining in stable disease while on therapy. No clear improvement in survival was demonstrable. In contrast to the disappointing response rates the overall level of toxicity was very low with no treatment related deaths. It is concluded that modifications in treatment schedules are required before further similar studies are commenced.

Thyroid dysfunction can predict response to immunotherapy with interleukin-2 and interferon-2 alpha

Thyroid dysfunction is a well-recognised side-effect of treatment with interleukin-2 (IL2). We assessed the correlation between the development of abnormal thyroid function and tumour response in 13 patients receiving IL2 and interferon-2 alpha (IFN2 alpha) for advanced malignancy. Seven patients had normal thyroid function during treatment, and all of these patients have since died of progressive disease. Of six patients who did develop thyroid dysfunction during treatment, one patient has died of progressive disease. However, statistically we were unable to confirm a definite correlation between the development of thyroid dysfunction and survival in this small group of patients.

Effect of the intestinal flora on the urinary organic acid profile of rats ingesting a chemically simplified diet

In order to estimate the influence of gut bacteria on animal metabolism, the excretion of organic acids, as monitored by gas-liquid chromatography, was compared in the urines of conventional and germ-free rats. Rats were maintained on a chemically simplified diet in order to minimize the effect of strictly exogenous compounds on the organic acid profile. Initial analysis of the excretion rates of 68 compounds, found reproducibly in the profile, indicated significant day-to-day and rat-to-rat variation, suggesting that haphazard comparison of experimental groups of animals might yield spurious differences with no biological significance. When repeated measures of the profile were analysed by a random effects analysis of variance model, no compound was found exclusively in the urine of either conventional or germ-free rats. Nevertheless, tricarballylate was significantly higher and both tartronate and vanillate significantly lower in conventional rat urine. The flora was implicated in these differences because caecal contents of conventional rats were found to convert such tricarboxylic acids as cis- and trans-aconitate to tricarballylate and to cause the dissimilation of both vanillate and tartronate, the latter compound being of dietary origin.

Urinary organic acid profiles in fatty Zucker rats: indications for impaired oxidation of butyrate and hexanoate

The urinary excretion of 45 organic acids, monitored by gas-liquid chromatography, was compared in fatty (fa/fa) and lean (Fa/?) Zucker rats maintained on a chemically simplified diet. At the age of 6, 16, and 22 weeks, fatty rats excreted more of the various organic acids than their lean counterparts. However, the greatest difference was in the excretion of ethylmalonate, even when excretion data were normalized to body weight. The next highest excretion difference was in adipate and an unknown compound, and the third highest in pyruvate. A second group of rats examined at 7 weeks also excreted an excess of these four acids, as well as glucuronate and indole-3-acetate. The excessive excretion of ethylmalonate and adipate, which is characteristic of human genetic defects in short- and medium-chain fatty acid oxidation, suggested that the oxidation of butyrate and hexanoate might be impaired in the fatty rat. Thus, as a test of their capacity to oxidize medium- and short-chain fatty acids, two groups of fatty and lean rats were transferred to diets enriched with either trioctanoylglyceride, a medium-chain triglyceride (MCT), or sodium butyrate, a short-chain fatty acid. Both lean and fatty rats on the MCT diet, but only the lean rats on the butyrate-enriched diet, increased their excretion of adipate. However, on both the MCT and butyrate diet, ethylmalonate excretion increased only in lean rats, almost reaching amounts found previously in fatty rats. These results suggest that the fatty rat has an impairment of the beta-oxidation of butyrate and hexanoate, a defect that might increase intracellular concentrations of butyryl-CoA, the optimal primer for the synthesis of long-chain fatty acids.